Parents registering babies in Cheltenham and Tewkesbury can also apply for their newborns to have their own library tickets.
If the three-month pilot scheme is successful, it will be rolled out to other libraries across Gloucestershire.
A county council spokeswoman said the library service had plenty to offer even to its youngest members.
"There are bright books to stimulate their sight, hearing and touch as well as nursery rhyme CDs," she said.
"We also run baby bounce and rhyme sessions and toddler story times.
"The library is a great place for families to spend time together and many of them even have children's centres based within them.
These are a fantastic resource for parents with children under five. We hope this scheme will encourage more families to go into their local library to see what it can offer them."