This topic came up in a forum recently and though I gave a short answer there it inspired me to write a blog post about it.  The post includes basic ideas for including children in rituals, a sample ritual complete with music, hands on ideas, and a game.

You can find the full post here...
http://ravenrinspagannest.blogspot.com/2012/02/including-children-in-esbat-rituals.html