Our experience:
0m: Portuguese and English as main languages and a little bit of German from some part of the family
3m: we started to do activities from the book Slow and Steady Get Me Ready
4m: Sign Language and some Leapfrog Videos like Phonics Farm
5m: he started attending a full-time school / day care (we had no option since me and my wife work all day)
6m: We started reading and pointing words on books
1.5y: just know I see that there are some regular programs for Maths, Reading and Music, so I'm starting now.
Before that, I always used to teach maths counting steps, things, etc.
For music I had nothing serious beside of singing. We also had him to watch our Choir trainning from 2m to 9 months.
By the way, this topic is a great idea!