What age and physical requirements does rafting generally have for children?

According to regulations, children under the age of 12 and under 1.1 meters are not allowed to participate in rafting. But if the children are in good health and under the protection of two adults, they can participate in rafting at the age of five or six. The drifting water is very cold. I am afraid that the children will not be able to bear it, and they will catch a cold when they go ashore. Another issue is safety.