Not specifically about homosexuality but I remember talking to my mother about this (she works in primary care, in Britain) and asked her how children dealt with minorities or things they weren't used to. My mum has had disabled people on her course and people of all races and creeds, and she has had to place them with primary students, often to the protests of the parents.
What she found is that children often don't judge at all, unless their parents are really obviously racist. In all her nearly thirty years of teaching experience she's only had to deal with the children of parents who she later found out were insanely bigoted. A normal child will be interested, and want to find out more, children are naturally curious, and it should be a parent or teacher's job to help them understand things.
For some expamples:
A black woman goes into a rather elite Norfolk primary school, (she was from somewhere in Africa, very dark skinned and with a pronounced accent as well). Not one child was mean to her, they just wanted to know about where she came from and what her accent was and why her skin was dark. There was no malicious intent behind it, they were just curious because, it being the sort of school it was and Norfolk being the sort of place it was, they had never been in close proximity to a black person before. According to the woman, it turned into an entire hour talking about other cultures around the world, and filled in for their 'religious education' lesson as well.
A woman who lost her arm when she was a child after an accident goes into a school, and again all she has to endure is some very curious children asking why she doesn't have an arm below the elbow.
Children aren't as prejudiced as people think. A prejudiced child is almost certainly a sign of prejudiced parents. If a child saw this on the BBC and asked their parents about it, normally I would say it's the job of the parents to explain what's going on, but I don't think I'd want these parents to explain personally.