Yea they will get some size to them, if they are left there to feed. They won't grow as quickly as the river fish, I don't think.
I wade a few creeks around here too, and have found one creek that has some good sized Crappie in it, 10 to 15 inches (biggest we have caught while wading creeks has been just shy of 2 lbs.!). They are trapped, they can't go down stream because of a huge obstruction (log jam) and they can't go upstream because the water is too shallow, but the spot is about 400 or 500 yards long, and about 30 yards wide, and ranges from no depth to about 7 foot. I caught a 6 lb bass out of it last summer, and several 3 and 4 lb'ers. Alot of big Gar in there too, maybe up to 24 inch long, and a few big catfish. This creek, before it was obstructed (log jam) flowed all the way to the Flint River. We have turned all of our fish loose, that we have caught there, so save them for somebody else to enjoy one day.
When we wade these creeks, we'll easily catch over 100 fish, everything from Bream, Bass, Crappie, and Pike. All on the same lures, and we'll wade a couple miles then turn and come back. The most fun (while fishing) I have had in years!!