We made all sorts of instruments available to discover and then left them to play.We wired open our piano lid so there wouldn't be any trapped fingers, left out a cheap guitar which was just for them to play. We left a very small keyboard on the floor, made shaky things together from tins filled with rice and pasta and enjoyed trying to change the sounds by filling them with different things. A cupboard in the kitchen was left without a lock and filled with tins, tupperware boxes, spoons etc. for them to get out and play whenever and however they wanted - as long as it was safe!. They joined in - whether invited or not- when we were singing and playing and enjoyed using a child's tape recorder and microphone on their own to perform into and then listen to. We recently discovered some of their own songs, from when Sarah was 5 and Kathryn was 2, on an old cassette. They remembered the day they made them up and recorded them. I'd never heard them before!
We didn't attempt to teach them because we felt that would take away the sheer joy and spontaneity of making their own sounds.

as you can imagine,our house was (and still is) absolute bedlam! Those were the days!