Here’s a cute YouTube video of a little Catholic boy playing priest. Traditionally, this sort of play was supported by parents (as you can see) with costumes and Mass sets, in the hope that the boy’s desire to play priest would grow into either a priestly vocation or a devout Catholic layman.
But yes, the play was originally the little boy’s idea; the Mass playset with chasuble came afterward. In the comment box, the dad says, “Isaiah is enthralled with the Mass and goes around the house consecrating everything from Waffles to milk to Cheez-It’s so we wanted to get him something a little more appropriate.”
Unfortunately, the combox not only includes delightful comments recalling priest play methods past, but there are some very mean-spirited comments toward the kid and his parents. So you might want to prepare yourself for the nasties.