"in league with the law"

Tonight was the rehearsal dinner for Auntie Sue's wedding and all the out of townies as well as us wedding partiers were there. The most adorable was her former roommate's eight-year-old daughter who told us a joke she made up herself and told us in her 8 yr old english accent.
"What do you call a flea that's in league with the law?"
"A po-lice-man."