There must be more to the story here. The sexuality of a fictional wizard is not very relevant to the readers of children's novels.
Telling us that Dumbledore is gay does, however, lead to some interesting conversations. My seven year old son heard me mention the story about Dumbledore, to my wife, and asked what it meant for Dumbledore to be gay. I could see my wife grin as I explained that Dubledore loved men romantically just like I loved mom romantically. My son then asked me which man did Dumbledore love? I said I did not know. He said he would have guessed Dumbledore loved Harry. Pause, pause, well... I explained that "romantic love is a different kind of love than the love he has for Harry. I romantically love mom while I love you just as much, but differently. Well adjusted adults love children but do not romantically love children." Oh, he said.
When my son left the room I asked my wife how I did. She thought I did quite well.
Here is more on the subject from Salon