Children can be very cruel. Even at 4 years of age, children notice and comment on differences- sometimes innocently but occasionally with intent to bruise. Whether it's a man on the street who 'walks funny' or a peer with a different family structure, children who are seeking a position at the top of the kids' pecking order will often see this 'oddity' as an opportunity for misguided sport.
It's particularly difficult to explain sexual preferences to a young child. One year I had contact with a preschool group which contained two children with alternate family structures- one with lesbian parents and one with a transsexual parent- and the same group was rich with alpha male children who decided to use these children's differences for target practice.