So he has his own apron (after all, messy has its limits, right?!). Whenever my husband or I start cooking in the kitchen he loves to run, grab his apron, slip it over his head, and pull up a stool declaring "I want to help". The apron I found at Williams-Sonoma one day. Of course I let him choose. Thought for sure he'd go for orange or yellow as he tends to prefer those colors. It's red. A red apron with cars on it. Oh, now the red makes more sense.
A Learning With Books activity we did as part of Flowering Baby age 3 (and I think it was in the Sonlight P3/4 manual too, but would have to check) was read If You Give a Mouse a Cookie and bake cookies. We whipped up this recipe: http://allrecipes.com/recipe/best-big-fat-chewy-chocolate-chip-cookie/detail.aspx It was pretty tasty. Mixing by hand may be a bit more work, but worth it when involving a little one.
Mix the dry ingredients in a large bowl, and then the wet ingredients separately. Measuring practice is great number practice. There's also fine motor skills practice as you learn to pour into containers.
Then make a well in the center of the dry ingredients. Pour in the wet ingredients.Time to mix!
I ask again, is adding the chips the best part? Yum!
Does your child actively help you when you bake cookies?