Autonepiophilia.

Autonepiophilia: sexual preference for taking on identity of an infant.

This is from a somewhat patronizing documentary on women and kinks.

It appears that for Kailey, dressing and acting like a baby is a way of experiencing what she felt she missed as a child, rather than a source of sexual arousal. As Kailey notes, if she and her boyfriend start having sex while she's taking on the role of Baby Ella, she switches back to Kailey. Her boyfriend definitely finds Baby Ella, and their play together, sexually arousing. Still, the documentary does leave open the possibility that Kailey is also turned on by playing the role of Baby Ella. And she does report being into BDSM.

And a bonus video: