The University of California - Los Angeles Special Collections Library has a huge collection of baby books collected from a variety of places. The library's blog has a post from February 14th, that is titled "Grow(ing) Up! The UCLA Library Baby Record Books Collection." This year is the 10th Anniversary of the beginning of the collection.
The post's last paragraph states "The books and their handwritten and pasted-in contents have been used for research and teaching in pediatrics, printing history, economic and social status, material culture, linguistics, architecture, advertising, folklore, depictions of family, and other topics and disciplines." I sure hope that the other topics include family history.
One baby book item I found in the UCLA Library catalog:
- Baby birth announcements, height and weight chart, and photographs for Charles Wriggins Walker, born 14 February 1914 in Buffalo, N.Y., 1914-1920.
A quick check on ArchiveGrid.org for the phrase "baby book" shows 385 entries. Keep in mind that some hits in any catalog might yield books on how to care for a baby!