Incest per se isn't one of my squicks -- sex between adult (consent) and child (dubious consent) is. Anything where one partner is adult and thus understands all the implications involved in the sex act - and one partner is too young to understand - that's just abuse, whether the partners are related or not.

Sex between people of a like age, on the other hand, is less objectionable so long as they're fairly close to age of consent. Child sex just does not turn me on at all. I can easily see teenagers at boarding school experimenting, and find nothing abnormal about that situation, even if they happen to be related.

Fred/George? Somehow I think these two have been naughty since their hormones first started percolating!