Give them a bit more time to grow up, especially if they're a smaller/more docile breed. Can he get next to their area when the babies are penned? That might help. You're going to have to show him that the babies are yours & not to be messed with. The whole carry him, chase him off, etc. You could try starting with 1 chick, let it out &/carry it with you. I've got 1 of the babies that I just had to bring back inside. I let them out last weekend (about 2 months old) & he's been chased/picked on so he went into hiding. Not sure he came out for food/water given his eating once he was inside. I'll be making a timid bird area for him & probably the crevecoeurs as they seem mellow. I've been chasing off, etc from the babies & the boys being too rough with a girl too. I've also pinned, carried, bopped on the head/beak, etc anything & everything.