Kneel astride the victim, place the heel of your hand against the upper abdomen, then place your other hand on top of the first. Press with a quick upward thrust. With opposing fists locked together, jerk in and upwards sharply five times. But as a rule, handle near-drowning victims very gingerly. Submersion in cold water quickly leads to hypothermia.
Rough treatment can trigger irregular heart rhythm, leading to cardiac arrest.
Don't assume it's too late, even if he has been underwater for a long time. Some children have been revived after being immersed in icy water for more than an hour. Continue CPR until help arrives. Once circulation and breathing are restored, warm the victim up to stave off hypothermia. Sharing body heat in a sleeping bag is one of the best ways.