When tested with an XRF instrument this 1958 Little Golden Book (1958! Same age as my husband!), tested positive for 208 ppm Lead (Pb).
Newly manufactured Items intended for use children today (in 2019) are considered unsafe (and illegal if newly manufactured) when they test positive for lead at 90 ppm lead (or higher) in the coating or 100 ppm lead (or higher) in the substrate.
Given the potential risk of lead exposure from vintage books, I have chosen not to have any in my home.
Most post-1980 books I have tested have been either Lead-free or Lead-safe, with a few exceptions. Here’s one notable exception (a book from 2006 that is very high Lead!) To absolutely avoid all Lead in children’s books, consider only purchasing books for children that were printed in 2011 or later (after the Consumer Product Safety Improvement Act was fully in place and enforceable.)
As always, please let me know if you have any questions!