The Yen and Ciri mods are up and work well, I will be adding different diapers in the next few days for each characters.
To help use the mods, I suggest you download The Witcher 3 Mod Manager
A cool mod to use with this game is the Multi Companion Mod, you will also need the Debug Console mod, look into the descriptions on where to place the files. With this mod, you can summon any NPC as a companion, so you can have diapered Yen and Ciri follow you around.