I Recommend "little people" flip flap books by Fisher Price. We have 4books of this series. Each book has 40-50 flaps. My daughter could remember all figures behind the flaps.
The other one I strongly recommend is "first little readers" by scholastic. It has a,b,c 3sets of books. There are 25books in a set. Total 75 books. Each book has one topic, one picture and one simple sentence per page. It's easy for Bb to understand what is talking about.