Sisters First tells the story of a young girl who wishes for a new sister. The baby cant do much at first (because #baby) but, over time, the two become best friends. Together, they feel smarter, kinder, and braver than they ever thought they could be.

The Bush twins just went on The Tonight Show with Jimmy Fallon to talk about their book. Barbara said they talked about writing a childrens book for "several years," but they finally decided to do it after trying to get Jennas daughter Mila excited about the birth of Jennas second child, Poppy.

"We told her all these fun stories that we used to do," Barbara said. "And we got excited thinking about a childrens book about how having a sister has made us braver than we ever thought possible, and its made our lives so much bigger and better to have a partner to go through life with."

Jenna chimed in that the book isn't inspired by their own experiences, but is ultimately about "sisterhood," which she added can apply to friends and colleagues, too.

Watch Jenna and Barbara's full interview with Jimmy:

This isnt the first time Jenna and Barbara have written a book together. They also co-authored the adult book, Sisters First: Stories From Our Wild and Wonderful Life , which was released last year.

It's been a busy 24 hours for Jenna: Not only did she release a new book, but she returned to co-hosting Today with Hoda & Jenna yesterday after being on maternity leave with her third child, Hal .