This isn’t an addiction, it’s just part of BDSM. Ever heard of something called DDLG (or DMLG, depends on her sexuality)? It’s where one person acts like a small child, plays with stuffed toys, sometimes wears diapers, dresses in childish clothes and is quite immature, and the other person takes on a sort of parental figure role and acts like a guardian to the Little. This kind of relationship can be sexual, but doesn’t have to, and both of the people are adults.
Well that’s your fucking opinion and please keep it to yourself. I personally don’t engage in the lifestyle, but I respect people who do because everyone has their own fantasies and kinks. If both of the people involved are happy and consenting, you are in no place to judge