You're going to need books from the "Freedom" talent books to max out Childe's abilities. This series consists of Teachings of "Freedom," Guide to "Freedom," and Philosophies of "Freedom." You can find all three as drops from the Forsaken Rift domain located in Mondstadt by Springvale.

If players wish to level up Childe's talent to level 10, they will need 9 Teachings of Freedoms, 63 Guide to Freedoms, and 114 Philosophies of Freedoms. These materials are obtainable from Forsaken Rift - Domain of Mastery: Frosted Altar on Monday, Thursday, and Sunday.

Childe Genshin Impact Talent books can be found in 3 drops from the Forsaken Rift domain located in Mondstadt by Springvale. But you should also know that your rank should be higher or equivalent to Adventure Rank 27. So that you can access the domain. You have to visit the Rift every Monday, Thursday or Sunday to secure the drops.