Things like forcing a child to make a life-or-death decision and the idea of becoming a father hurt Sieh far more than being sexually abused. And he has no problem at all having consensual sex, even if he seems to do it more rarely than most of the other gods. That's because the first two things force people to grow up, while being raped just leaves people feeling helpless. The description of "losing one's innocence" only applies in societies that think all sexual knowledge should be hidden from children. And contrary to widespread ideas created in the Victorian era, most children do have a libido, even if it only shows itself in the form of masturbation (which even embryos in utero do sometimes). Besides, Sieh's definition of "childhood" does seem to include puberty, even if he prefers the form and mental attitude of a still pre-pubescent boy most of the time.
It's mentioned that Itempas and Nahadoth went to war the moment the former emerged from the Maelstrom, and continued that war for eons until it eventually became love. This helps explain why Nahadoth and Enefa cutting themselves off from Itempas drove him mad. Nahadoth, as the first God, had eons of experience as the sole occupant of existence to give him practice with a life beyond his relationship with Itempas. Enefa, as the third, had to deal with sharing her siblings' attention from the outset. But Itempas, from the moment he came into existence, had never known a moment in which he was not the center of Nahadoth's universe one way or the other and had no frame of reference with which to deal with such an occurrence.
Also, just as in the real world, quite a lot of children probably are being beaten and molested in Sieh's world. So being a victim of abuse, no matter how awful, is part of his domain as the God of Childhood, just like fatal diseases, bullying, and monsters lurking in the dark.
