Two kids with the same Apple ID and I need to separate them
I bought an iPad for my daughter and used my apple ID to set it up. Then the following year I bought an iPad for my son and I used my own apple ID again. Didn't know about the family sharing at this stage. Now both iPads have the same stuff on them as if one takes a photo or downloads an App it pops up on the other iPad. they keep deleting the others persons stuff and are killing each other over it. How do I change the ID on one of the iPads so they are no longer linked? Any help is appreciated but please make it simple for me. Thanks in advance
iPad, iOS 13