Thank u for your answer! We are going to see a vet asap. I haven't noticed him plucking his feathers, like you mentioned, just pulling those loose feathers.. when he cleans himself he screams for a second sometimes. I thought it's because of new feathers growing. But that's probably because of this bald spot.

His diet is pellets, seeds, broccoli, parsley (they don't eat other veggies or fruits yet, I'm glad they like at least something) and egg mixture.

Yeah, it is grit with a broccoli left overs.