I don't have any problem with it in theory... Unfortunately, there are realities which need to be addressed... The sort of realities, for example, which mean that no male teacher would ever meet a female student without making sure there was also a female teacher present. The fact of the matter is, a baseless accusation will ruin lives, and when it comes to sexual predators, it's not even a case of guilty until proven innocent... It's guilty even if proven innocent. Even if, as someone suggested, you recorded every session, it's just too risky. (by the way, if you do record stuff, make sure you inform all the players and the younger ones' mother.)
It'd be one thing if it were a family member or even if you were good friends with the neighbor, but judging from the fact that you didn't even know about what age the girl was I'm guessing that's not the case. There's just too much risk there, I'd recommend against it.
Of course, that's just my $0.02 on the matter.