I am guess when you say perch you are referring to members of the sunfish family and not yellow perch? I still get confused with all the local names of fish!

It is really hard to tell whether they are RES or CNBG... But if your RES were 2-3" in April, they were probably a bit on the small size to have spawned. However, 3-5" CNBG would be large enough to spawn, so I would put my money on the little buggers being baby CNBG. If you can net a couple and take a photograph, we can confirm or deny my suspicion.