Yes some Collies will herd anything....given the chance.
It is a natural instinct and in some cases can be encouraged but not herding children, cars bikes etc.
Look at the general balance of your dogs life- a collie needs a lot of mental stimulation and some exercise. Too little mental stimulation and a collie will go self employed.
Check that your dogs daily needs are being met. Do you do any dog sports with your collie or does he have regular brain and training sessions (daily) plus a good long off lead hike?
If your collie is mentally stimulated you may find that he has less time and energy to find his own entertainment.
If the children are running around as they have an absolute right to do
pop your collie in a quiet place with a bone and leave him be.
Do not let the children play any chase or "aggressive" high energy games with your dog - they can play fetch, hide and seek, train tricks, or tug under supervision.
Get the children involved in clicker training of your dog and get them teaching him tricks.
The second your dog does go to nip stand still and quiet and stop all interaction with the dog. If he continues to nip remove by his collar to another room - say nothing if all the family do this consistently he will soon learn nipping no interaction, no nipping lots of positive interaction.