Work on manipulatives. Make up a staff starting with the trebleclef and practice note placement. First colors, then move to black. You can use a dry erase board, magnets, paper, whatever.
In a way that is fun but not stressful, play games with the knowledge learned from LMs. Take turns recognizing notes/chords....you place and the child guesses, then the child places and you guess. You can have them choose from two different flashcards too (Can you point to the Do-Mi-So chord? Which one is Fa?) You can color the notes on the staff using the solfege songs. If you have not yet memorized any, that is a very good thing to do. Then replicate them on the staff using magnets/crayons, or on a basic color coded instrument like a keyboard or xylophone. Just use some office supply colored dots or color some white ones yourself and stick them to your piano, xylophone, etc. You can play with colored legos and put legos on a staff or make a custom lego board staff, play games with m&ms or skittles just for fun. You can introduce the curwen hand signs and have the kids practice singing their nursery rhymes in solfege while signing and print out the chart to have them use as a coloring page...the possibilities are endless.
If you are looking to teach your child how to play an instrument, it might be a good time to introduce it. As for other programs, I really like Themes to Remember, Piano Maestro is great, Yamaha piano classes are WONDERFUL, and the Preschool Prodigies music program (hand bell based) on kickstarter looks really promising.
ETA: I initially did not realize that you have been doing SM and some of these things may not apply to you or your child may have already mastered them. I am going to leave the post anyway for others who are wondering the same thing.