He thinks he's the boss and even though he's little, he can do some damage, especially to children. Beekissed article is the most often cited and it works, but you gotta be consistent. I've found what's most important is don't show fear and you control the situation. Don't let him control what's happening. Do what you have to, to force him to recognize you are in control. For example, my roo is protective if I mess with his girls but he's slowly learning they're ALL MY chickens (including him). I pet his back and wiggle his comb to embarrass him, shake things near his face to make him back up if I have to (he's scared of new looking objects even if they've been there for days), etc. And if I want to mess with his girls, I will do it while he's in the coop and can't do boo about it. If I need to pick up a pullet next to him, I've even waved the girl in his face, using her as a shield. He calms down if the girls are calm, and he hasn't gotten any funny ideas since I started this training. In the end, roosters are just big chickens! Literally!