I think it must be genetically hardwired into most little boys to love that stuff - because I don't think I've ever met a boy that age that wasn't obsessed with legos and at least one mechanical thing (cars, planes, trains, robots, rockets). It's kind of weird because we didn't do anything to encourage this - his toys were all pretty generic baby toys, and gradually he started gravitating to the blocks and legos and ignoring the stuffed animals and people all on his own.