Essentially everyone does that, best thing is to not let the thing get out of control so that someone phones the cops.
Also if an adult or 20 are there technically it's a little more hazy, private parties aren't covered the same way legally, I believe minors can be given drink at a private party as long as they are over 14, the only time I think police will get involved is if all hell breaks loose. Last time that happened to me, they arrested the people involved who were still there and by then most people had left anyway, but then most were just shy or over 18 anyway.
Frankly what happens in your house so long as it's not bedlum is your own affair, within reason.
By the way I'm no legal expert so if this is wrong and you spend a night in the cells, you aint seen me right?