This is most likely a minor sprain. Give your child motrin to relieve the pain and tension. If in a couple days the problem is still there see a doctor or a chiropractor.
You should apply moderate heat. Either a compress such as a dampened wash cloth (warm but not hot water) or an electric heating pad. It should be better by morning.
Try massaging your childs kneck, as well as rotating heat and ice packs to reduce any swelling and prevent muscles from knotting up. If the pain continues take him to your doctor to rule out a pulled muscle.
The proper advise should be taken from a physciotherapist, for such cases. We have to take proper care for kids, as their organs are delicate. Remeber we should not neglect such cases.
