DS loved the Thomas train puzzles from Ravensberger when he was 1.5-2 years old. I think we have a few 24 piece ones, couple of 35-40, a 48 and a 60. The Thomas puzzles have bright cartoon colors and are easier to put together than a landscape one where the background looks all the same. DS could do a 100 piece Thomas puzzle at 2, but couldn't
(or wouldn't) do a 100 piece puzzle with 2 horses in a meadow even at 3-3.5. I would highly recommend the 100 piece glow in the dark Thomas puzzles. For added challenge, you could always mix together multiple puzzles.
DD is 3, she can do all the Thomas puzzles, but she isn't really into them. We found a couple of fairy/ballerina ones (we don't allow Disney princesses in our house!), but there's not that much to appeal to girls. Somehow, puzzle makers seem to focus on boys
