Boy and girl teen party ideas? 12-13?

ok so im having a party with boys and girls aged between 12-13 , its gonna be a little awkard with mom and dad around..yikes :/ :/ , My house is around 10 mins away from 2 beachs ( FEW PEOPLE IN MY CLASS DISLIKE THE BEACH) amm dont know if everyone is coming ill be inviting around 16 , i cant think of anyhing to do that we will all lke , this is party will be after a water fight ( last day of school we have a water fight) so please as you can see im forward thinking because with around 16 boys and girls coming im gonna need to start thinking now!