Flatheads are nasty predators on sunfish. They are also nasty predators in bullheads and well anything else they can fit in their mouths!

Depending on if you wanna drop the money, fyke nets would be a good option to remove large numbers of bullheads. They also make traps designed to catch catfish, but I think the fyke net is more effective. However, you will have to sort out the other species of fish you catch that you don't want to remove...

A healthy population of bass to aggressively feed on the young bullheads should keep them under control. It is imperative to keep them under control now. If they get too numerous they can cause water clarity issues and make the bass option less viable as the water will be too murky for the bass to effectively feed on the bullheads. CC in the larger size range also prey heavily on small bullheads IME as well.