Water Blocks Let You Mix Colors without Making a Mess

There’s still something to be said for smooshing together an entire tray of watercolors, but if you’re looking to teach the kids about color mixing without making a mess, Water Blocks can make the job easier. The set includes square and half-circle blocks that hold water in the three primary colors — red, blue, and yellow — but when you hold the blocks together, you can watch the colors change and swirl while safely contained in their windows.

$39.99 from ThinkGeek.