No, he is not taking formal lessons yet.  There is not a Suzuki school in my area, or I probably would.  I do play myself though, and have made an effort to show him little tips here and there.  He now knows how to hold his bow and violin properly, and to play individual strings.  I have to be sneaky about tuning his violin though, he is very reluctant to let me hold it.  He pulls out his violin two-three times a week, which is more often than I pull mine out.  Right now I'm happy with his progress with it being a "toy" for him to experiment and play with.  We are doing other musical activities in our home, and violin is more of a side program.

I just barely saw this thread, so I'm jumping in now.  This is a subject I'm rather passionate about.  My music background is somewhat extensive as I got my degree in Vocal Performance.  I have always planned on homeschooling, and music was always going to be a "core subject", right along with the four 'R's, (reading, writing, arithmetic, and religion).  So I think that music is EXTREMELY important.  My goal isn't to turn my children into little Mozarts (although that would be really cool!), but to give them a solid background in music that can enrich their whole lives.  Hungary has been very successful with their Kodaly method, and I use it a lot with my own children.  To briefly summarize what we do, my son owns a violin (no formal lessons yet), we play with percussion instruments, we listen to classical music, I am teaching them to read rhythm, we have singing time almost every day, and I favor children's books that I can sing (not just read) to my children, like nursery rhymes, or my son's favorite, "Puff the Magic Dragon".
I have written a few articles about our music program that can be seen here:

http://www.professional-mothering.com/music.html

Thank you!

It has been brought to my attention that "Give your Child Genius IQ" is actually currently unavailable for purchase online.  It is an update from his earlier book, "Raising Brighter Children", and is very similar to it.  Things he recommends doing with your children include easy mazes that become more challenging (We have used Kumon's workbooks with great success for this), placing a few items in a basket, letting your child look at them, and then you take one away and they have to guess which one it was (a memory game that is easy to make more difficult by adding more items), looking at those similar pictures to determine what's different about them, and things like that.  He recommends using the educational video media at the library for your screen time.  He talks about placing maps on your wall for your childrens reference.  He suggests simple counting games.  Many of his ideas can be played in the car while you drive and they have some sort of manipulative in front of them, like magnetic letters on an older baking sheet.  He also talks about his reading program in this book.  I too have recently blogged a bit about it here: 
http://www.professional-mothering.com/phonics-for-toddlers.html 

I actually didn't have that much luck using it with my 2-year-old, and I am trying the whole-word method again with him.  It's a little bit frustrating that of all of the early-learning programs I have wanted to implement in our home, reading is the one that I wanted to succeed at the most, and it is the one that hasn't worked for us yet.  The success we have had in all of the other programs, including from Glenn Doman and Sidney Ledson, has more than made up for it though.  I highly recommend Sidney Ledson's books.

There are some very cheap violins available on the internet, and if you rent a violin you could end up paying a lot more.  We bought a violin for Peter and he loves it.  We are still not giving him formal lessons, but he knows how to hold it, how to resin the bow, and takes really good care of it.  I also play and show him little bits here and there as he lets me, but he's very protective and I have to be sneaky just to tune it.  For more information, I made a post about it here:  http://www.professional-mothering.com/violin-for-toddlers.html

If you use it, you certainly didn't waste your money!  Xylophones have a duller pitch than glockenspiels (Xylophones are made of wood and glockenspiels are made of steel), and that's what I bought for our family, but I think what you bought looks like a good one.  The advantage of the xylophone is that you can teach your kids to read music with it as well.  Orff Schulwerk uses mallet percussion a lot in their methods, you might look into it to help get the most out of your purchase.  Good luck!

The one we use is called Goodreads.  I love it because I can put books on different "shelves" to help categorize them better.  It's a great site.  You can become "friends" with other people on goodreads and see what they are reading, reviews they have posted, and share your own reviews.  http://www.goodreads.com/

I'm really glad you shared your review.  And as a music graduate, I can certainly attest to what the Dr. says about solfegge.  I really wish I had been introduced to it before college.  The Kodaly method from Hungary is another one to look into for teaching solfegge to younger children.  I do wish to clarify that Si is only used instead of Ti in fixed Do, which is when C is always Do, D is always Re, etc.  When you teach movable Do, which is where Do is the the key note, then Ti is used.  Anyway, that's probably being too particular, but I wanted to clarify.  I've written an essay about the Kodaly method that you can see here, if anyone is interested:

http://www.professional-mothering.com/kodaly-method.html

I approached this issue backwards.  I was homeschooled, and was always planning on homeschooling my children.  When I became a mother I wondered, "what happens before preschool?"  I found Doman and then forums like this one, and am grateful that I can give my children a head start.  We will definitely be homeschooling, and we'll just progress from where we are.

I have posted pictures of some of mine here:

http://www.professional-mothering.com/encyclopedic-knowledge.html

If you purchase your own laminater (ours was $40, but I've seen them for even less at Sams Club), it is very cost effective to laminate them.  I buy 200 sheets for $20 at Sams Club, which makes it 10 cents for every thing I laminate.  I also use the laminator to make "toys" for my kids, it was an excellent investment.

Teach your child to read in 100 easy lessons and Sidney Ledson's book are completely different.   I love Ledson's books.  My favorite is "Give Your Child Genius IQ: A Program for Busy Parents".  It covers most of what the reading book does, as well as giving tips for teaching other skills, including memory and thinking skills.  I highly recommend it.  I've read several of his books, and they tend to be repetitive of each other, but "Give your Child Genius IQ" is the most complete.

When I was a music major, a few fellow students had perfect pitch, and they didn't really have that much of an advantage, except for in aural skills.  What you need to develop to be a good musician is RELATIVE pitch, meaning, if you start singing in one key, you end in the same key, you can stay in tune, and if you have practiced a song extensively, it feels awkward to hear it in another key.  Perfect pitch means you hear a F#, and you can identify it, or someone says "Ab" and you can sing it.  After four semesters in aural skills I sort-of developed perfect pitch, and if I wanted to I could get it back, but I don't see the point.  Perfect pitch is not an impediment, but a skill like being able to whistle loud, helpful in some situations, but not necessary for good musical development.

Great ideas everyone!  I second the idea of playing music.  One thing that makes music more fun, and encourages movement, is to give them a large silky scarf to twirl through the air while you dance to it.  I did this a lot with my toddler when I was very pregnant, and it was really fun for both of us.  I would demonstrate circles and high and low, and he would mimic me, and burn a lot more energy than me in the process.
You won't regret making a brachiation ladder, it has been a lot of fun for our family.

We got a violin for our two-year old on e-bay, and we have been very pleased with it.  It was $55 after shipping.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=180430504395

I made a video of him playing it, as well as a picture of it, that you can see here:

http://www.professional-mothering.com/violin-for-toddlers.html

I have written a little bit about it here:

http://www.professional-mothering.com/music-for-preschoolers.html

My oldest is two and doesn't have a lot of patience for any formal lessons yet.  I sing to him a lot, and I often will sing in solfege to both of my children.  I sing the major scale, and I'll sing simple nursery songs with the words and solfege, just to give him exposure.  Of course, I was a music major, and am kind of a nerd that way.  Before my children were born, I would do that for my husband, or while I was doing dishes, etc.  Much of what the article talks about is what I have done with my piano students, whom have been as young as 5.  I do use rhythm syllables, and I think for very young children that that's the way to go.  It's complicated for a young child to understand that "this is a quarter note and it gets one count", but to teach them to say "ta" when they see one, suddenly it's a concept that they can grasp.  I use rhythm syllables with my older piano students when they do rhythm exercises, but they also need to know it's a quarter note, etc.  We have also purchased a glockenspiel, and I pull that out a lot and let both of my kids strike the keys.