Breathing every 3 strokes during freestyle

My 10 year old son just started swimming on a non-competitive swim team this year. He mentioned in passing that he holds his breath while his face is in the water when swimming freestyle. He is not very fast right now, so it probably doesn't harm him now, but I would like to break him of this habit before it sticks! He said the timing of the exhale and inhale confuses him and he ends up choking on water. He breathes every 3 strokes and I've always learned to breathe every other stroke. How does the exhale/inhale work for every 3 strokes. It seems like a long time to exhale?