Just look up a photo of each signature on Google and then replicate. Yes, they are "actors" signing, but they do have training in how to sign for their character (so they all look similar year to year, person to person). At our resort we tried to have a trained character signature person on shift all the time to sign pictures to leave in rooms for special requests. Basically any cast member can take a character signature class and learn the main sigs, like the Fab Five and other popular characters.

As to whether your four year olds will remember that they need these books....I still have my signature books from my trips at that age (4, 5, 6, etc). They are all dated and I love having them.

So it is very possible they could miss these. And you could also contact Guest Services and explain the situation - I bet you could get signed photos to replace them if you want to be honest with your girl that they were lost. Either way will keep the magic going.