When my children were going to get a new sibling (and even before that and they were showing interest in babies!), the Anne Geddes collection was a favorite. It is whimsical and interesting, placing babies in costumes: bee, teddy bears, snail, butterfly, scarecrow, baby bird, mushroom, hedgehogs, and pansies.
I could point to them and start a whole story with each picture! Then they would keep it going :-) A great imagination starter!