I do not understand the need to restrict children of same sex marriages. It smacks of punishing the kids for the acts of the parents. Regarding the requirement for children of same sex marriages to disavow same sex marriages when they reach 18, why not simply require that of all children when they reach 18?
Did you see the comparison with children in polygamous Mormon homes?
As for the disavowing thing, it’s a good question. I personally cannot disavow it, and were I a convert seeking baptism, but I had it withheld for that reason, I would have a real hard time with that.
I think, however, that it’s important to determine both intent as well as behavior.