This happened to me also,my children have I touches & unbenounced to me ..........they were getting free games & upon playing them a in app purchase would show up. being kids they clicked on them & purchased many things . well I contacted apple support & they explained it like this.............. after the parents put the password in ,there is a 10 min window that the touch purchases will not prompt you for a password .
so now we do prepaid I tune cards.
@vistamike apple did refund the $80 the kiddo's rang up so all is well. twas a lesson learned