Hexbugs. 3 and up. Small, battery-powered, buglike tokens, Hexbugs move through environments kids can build out of plastic hexagons. Moving up, down, across, even flipping over, Hexbugs can show how well a designed environment works for its inhabitants. Add-on kits expand the range of possible environments. A small number of reviewers note kids can lose interest after building the habitats a few times and then just watching the bugs move around. Others say kids find enduring fun with Hexbugs. As they say, your mileage may vary.
Gears, Gears, Gears. 4 – 10 years. Simple principles of construction and mechanics underlie this collection of gears, cranks, pillars and connectors. The basic kit enables open-ended arrangements, and add-on kits contain parts for making specialized objects – vehicles, animals, scenes – by following instructions. Kids see how cogs and gears can be configured to drive motion and force across a field of intermediary parts. Some people report kids getting frustrated with add-on kits that limit the range of what can be built.