My mom bought my daughter a 24 piece puzzle when she was 21 or 22 months old. At first I thought my mom was a bit out of touch with reality, as I had never heard of such a young kid doing jigsaw puzzles like that. 3 days later I found myself taking a video of my daughter putting it together by herself. We bought her 3 more puzzles in the next couple of months, but at some point her interest waned.

Having said that, I am a big proponent of adding the third dimension when applicable, as it is something I've always struggled with. I'm much better at problems that I can reduce to 2 dimensions.

For her 2nd birthday, my wife and I bought my daughter the Battat Take Apart Airplane, as sort of a 3-D puzzle.



http://www.amazon.com/Battat-68024-Take-Apart-Airplane/dp/B000N5QNSK

She loves it. She can take it apart by herself, but she needs help putting it together. (She's 28 months old now.)

Her brother (almost 7 months) loves it too. He just spins the propeller or slides it back and forth across the floor though.