I don't mind kid!fic in principle but an awful lot of it is written by people who rather obviously don't know kids (particularly babies and toddlers) and I just read through it going "kids of that age, they do not behave like that." Usually they are way too old and wise for their years in a kind of cutesy way, but sometimes they are also way too young. I guess, like the presence of OCs, there's nothing inherently wrong with the idea of kid!fic but I do consider it a bit of a red flag so I'm unlikely to read kid!fic from an author I don't know, and I'm more likely to bail early if the story isn't grabbing me.