Yer jist a young whippersnapper at 59.
I can't say that I've tried marshmallows but in an over crowded farm pond most anything will catch bream. As a boy 55 or so years ago on such an over crowded pond I used little yellow flowers I pulled at pond side for bait and caught them as fast as I tossed the line back in. But then I caught several on a bare hook as well.
More recently at my own small pond we use a bait from Wal-Mart that looks about like a super tiny marshmallow really and has about the same consistency and it works just fine. I'd say as long as they are small enough for the bream to eat they'll work.