You are right to be concerned. An excellent place to start would be implementing some desensitization and counterconditioning at a safe distance. Perhaps feeding high-value treats when watching kids from behind a window at home or in the car. Then move to the yard safely behind the fence keep him leashed at a distance and keep feeding high-value treats for seeing the kids/hearing them. Afterward, for any closer "socialization" he should always be leashed and at a distance from the kids (under threshold), but because things can get risky here, you really should be working with a professional for safety and correct implementation. If you push him over the threshold, he may regress rather than improve, and things may get more challenging. The more he rehearses fearful behaviors, the more difficult to overcome. I would not expose him to very rowdy or noisy play, as it can stress him out.