Welcome to BYC! I would let your son watch several rooster crowing videos before you take him to see the rooster in person. I hope it helps with his fears 
Children can be afraid of the oddest things. My daughter was terrified of giraffes until she was 12 
Children can be afraid of the oddest things. My daughter was terrified of giraffes until she was 12 
We're so happy you've decided to join us
