A homemade Lava Lamp? I'm not sure it could get much better. A little bit craft, a little bit cooking, a little bit science and a whole lot of fun! Come Together Kids: 10 Crafts and Activities for Boys
DIY busy board full of switches, latches, and doo-dads for babies and toddlers to manipulate. This is great for fine motor skills. It is also a hazard for giving escapee toddlers the skills they need to get out unsupervised.