apple ID's?

Hello. When we got our first ipad and ipod touch they were for my son. I created an apple ID and this is my primary email. So its my (the adult) apple ID. It's what I use for Apple Music. My son has used this apple ID for his Apple devices over the years. So all of his pictures and things seem to be attached to this Apple ID. I have since created a new apple ID for him, but when we tried to sign him out of my apple ID on his device and sign in with the Child Apple ID we created, all of his photos, games etc were not there. Also, it seems to be linked in other ways. At one time, my gmail account was even logged in his ipod touch but I seem to have disabled that !!! As well, the two factor authentifcation etc. ---> instead of coming to my personal device(an Android) , it goes to his ipod touch or his ipad mini. So he is the one who has to verify /authorize purchases, for my other son, who has a child account set up properly with his own child apple ID. Is there any way to fix this, so that he is logged in with his own Apple ID but has everything up until now associated with my apple ID?