If group members are dependent on their parents to bring them to meetings, it may be necessary to talk with them directly. Try to be flexible, at least one group created more problems than necessary by setting the time and place for the meeting in stone. Groups of young people usually need a leader. The leader is someone who directs the conversation, proposes things to do, organizes future meetings and makes sure everyone respects one another by asking people not to interrupt, etc. Often what works is having each of the kids themselves be responsible for the activity of one group meeting.
Different groups have different focuses.
Some are exclusively about sharing problems, while others are extremely social, most do some of both. What your group does is up to you and the other members. Kids with lesbian and gay parents don't have any more problems than kids with straight parents, but they don't always have the same access to places and people to deal with those problems. Just being around other people from similar families is often the most anyone needs. The first few meetings, when you are getting many of your members, should start off with the introduction of the person who will lead the group.