I used to know someone that has a sexual fetish like this.
https://en.wikipedia.org/wiki/Paraphilic_infantilism

When I was a sex worker, I went to a clients house and when I went inside, his entire house was decked out in...baby apparel? There were cribs obviously manufactured for this purpose, and I saw clothes laying around the house like oversized baby clothes. So its not unheard of at all. As far as i understand, though, its usually something someone does with a partner and not with their family. Not sure. Anyways I thought id give some input.