why not? it's not like each of them are pervs and think about sex all the time, if you don't mind them, then you accept them, which means they are not a bad example, and they won't be bad examples for the children, it's not like you will be raised a gay, I mean you don't learn to be a gay, either you are or not.
If they will care about their adopted children and give love unconditionally, then where is the wrong part here?
There are single women or men adopt children too, they don't make a "perfect" family (mother and father). Are you against that also or just gay couples adopting children?