I'd say adult babies. I saw some Tumblr blog by a guy who was into DDlg. One day he was in the supermarket and overheard a little girl in the next aisle pleading with her mum to buy her a toy, and he got hard. He swore he wasn't a paedophile and had never thought about it before, but he realised he'd been conditioning himself to be turned on by kiddie things, and someone begging in a little girly voice. He'd developed a sort of Pavlovian response to it. He and his girlfriend stopped it straightaway and just did other sex and fetish stuff, basically to deprogram themselves.
So I see it as more of a gateway drug to paedophilia, or exploiting a sick coping mechanism for an adult who was abused as a kid instead of getting them actual help. With furries, plenty do abuse animals, but most of the time their fursonas are weird fantasy shit like dragons or wolves with tits and forty dicks instead of an actual domestic animal, so they're less likely to act out unless they have another nastier fetish as well.
Edit: Come to think of it, do you get age play that goes in the other direction? Like are there groups of dudes who fantasise about shagging grannies and make their girlfriends wear hairnets and cardigans? I mean there must be, but is it a thing in ageplay groups?