While I can't think of all the names off hand, the books boost Logic/Painting/Writing.
On first glance, it doesn't seem like they tell you, but in retrospect, they do.
Writing - Frank I'm Not (as opposed Sam I Am)
Logic - Squares Are Not Triangles
Painting - Handprints of the Masters
Also, each group has identical covers, so if you're not sure on one, you can check the other 2 in the series and see if the cover matches.
Each book provides a 1 level boost to the skill in question, and if you read them in the library to the toddler, it doesn't take any time at all.