I had decided myself that the other two curses could show up in children. It doesn't make much sense to me why the curse isn't supposed to effect children; as I recall, the initial reason back then was to sidestep the issue of how children could be effected by a curse that would have turned them into "sex-crazed bimbos".
In my head-canon, TGs do have their gender swapped (and experience some innate sense of wrongness for it), but only gain the ability to shift at puberty, and even then most of them rarely use it because of how uncomfortable it is (although some are more gender-fluid and sex-positive than others — not that medieval peasants would have the vocabulary for that).
ARs are trickier, though, because in most of the stories I read with them, they tend to present themselves at age 12 to 15 — about the time the curse manifests, which would seem to suggest that it just stops their aging process. The only other story I knew with an AR main character was To Snare a Rabbit, where the AR lead character stayed as a ten-year-old, though I had taken that as a preferred form rather than a default one, similar to Goldmark always being in near-feral form. I was thrown when I was reading elsewhere on the wiki about a default age of 9; this rose the question of whether the curse hits them at their default and stops their aging, or whether it reverts them at puberty to their default.