Look like golden plums to me.

If in doubt taste one. At least cut it in half and see if it has pips or a stone for a start.

I would guess that's a sucker from something like cherry-plum (Prunus cerisifera).

they look like crab apples to me. cut one in half if it looks like an apple with pips it is a crab apple. if it has a stone it could be a cherry or plum.