I am going to be the contrarian on this matter even though baby talk turns me off too. I think when your partner does something that you don't find sexy you need to ask yourself what they might find sexy about it. People usually baby-talk to babies right? I think that maybe he was just doing the psychological equivalent of dressing you in a babydoll nightgown. He was trying to make you more bottom, not trying to act bottom himself. So if you could see it that way you could respond by doing something like sucking on his thumb provocatively (my new favorite word).
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver