Puppets!!!
The root-vue garden. (we're trying with bean sprouts and a clear glass, but we've already killed one batch), tadpole hatching kits (we'll try after we quit killing the bean sprouts), butterfly gardens As Seen on TV.
Have them take pictures. 2.5 yr olds take fine pictures as long as you put them around nice things to snap (not the laundry hamper or up mamma's nose on the couch. c'mon folks- that's not cute, really.). Mine's documented local wildflowers and the playground equiptment, leading up to this year when I plan to have him photo document science projects for pre-writing journal practice.
Make a webpage. Don't be so perfectionist in making it. Just document your journey. I'll pm you mine. Yours will be better, I'm sure. This is nice to print out later to save samples of their work, but takes less space and is less likely to be damaged than hard copies. Besides with 6 of you it will be more interesting and full of ideas for other mothers.
A tip someone gave me for my wepage/forum posts/portfolio collection- people are more interested in seeing your kid's creations than they are in seeing their mastery of worksheets or cookie-cutter magazine crafts (I don't care, I'm impressed). So try to get a good balance at least, if you don't want just a child-led gallery, that's fine. Just a reminder.
