Ultimately the reason cold water drownings are survivable is because the lower temperature decreases the speed of chemical reactions. If chemical reactions are happening (e.g.) 10x slower, then the amount of damage that occurs 10 minutes after cessation of breathing at normal body temperature now take 100 minutes.

Unlikely. The issue is cold and the speed of the cold. Children have a higher surface-to-mass ratio along with less subcutaneous fat which allows them to cool quickly. The article quotes the breakpoint:

  If water temperature is >6 °C (43 °F), survival is unlikely for submersion >30 minutes.