I think it's easy to be duped into buying suboptimal toys, especially around the holidays. I was hoping for people to offer tips on the general psychology of children learning science at this age, so that those tips could be collected into a strategy for making a systematic and principled purchase decision. I can supply the details about my sister, but I don't know how to make sense of those details as applied to buying a toy to elicit a specific effect. I really think that 'rational toy buying' is appropriate. I was inspired by this post and was hoping to bring about a discussion that mirrored that but for purchasing educational toys. Lots of very useful advice and suggestions have been given, but my post fell short of my goal. Either way, I think my choice of title was relevant. I think it's very odd that so many LWers rapidly point out superfluous uses of "rational". I should go around to posts and point out superfluous pointings out of superfluous uses of "rational."