Hi,
thats sad news as he is clearly a pet. This time of year does bring the hormones to the surface but it sounds like he has a very dominant/ agressive temprament. Replacing him with a more docile breed may be the best answer. The two reasons for agression are defence and attack. Unless nigel warns you ( by standing tall and flapping his wings) and then you ignore this and do something which he sees as challenging then I would say that he is not being defensive. If you are nowhere near him or his hens, you havent supprised or threatened him or the girls then he is not deffending but attacking in order to drive any potential suitors away from his girls. Children often command less respect from animals and this can be due to the pitch and volume of their voises, erratic movements, eye level and appearing more submissive so this problem could continue. As a result he may be more likely to go for the children.
the pinning down technique will only work if you are in or can instigate a confrontational situation with him. The other important thing to remember is that this isnt a punishment its a demonstration of dominance and he must only be relesed when he submits. If you let go you must not turn away and if he comes at you again you need to pin his head down again by picnching the feathers at the back of his head. Dont be angry when you do this he dosent understand that he has offended you by attacking your children, be patient and dont give up until he turns away from you and when he does taking a swipe at a tail feather, following him, chasing him away and waving your arms will ensure that he knows that you won the right to his hens.
the problem with this aproach on cockerels however is not that they forget but rather that the male sexual drive is is stronger than that of females which means that he is programmed to continue to challenge the dominant male ( thats you) to achieve the right to mate with his hens. The other difficulty is that no sooner would you put him in his place than you would diapear and leave him to take up his dominant position with the hens again.
good luck with him.
Buffy.