I think you handled things well. Although if I was gaming with an adolescent whose parents I did not know well, I would be tempted to produce a consent form to be signed by the parents (in my presence at that). Like others have said, in this lawsuit-happy time, it pays to be safe; the consent form ensures that everyone is aware of each other.
It would probably be wise to also make sure you had a female grown person in the vicinity. I sometimes serve in our church for supervising the temporary housing of young people who are in dire circumstances... and because I am male, our rules state that there must be another person (female) with the male supervisor, or two female supervisors. I guess they feel (probably rightly) that females are safer. One could understand why a church (or similar organization) might impose such rules (especially as I am Catholic), given recent events.
That all being said, I think it wonderful to include young folks into these activities. It is certainly better than Television, or semi-mindless video games, or many of the other activities that they might use their time otherwise. Good Luck.