I really really hope this is a legitimate "I don't know the answer" and not an "I told you so" question. LOL
But yes, it is WAY too cold. Something hubby may not have thought about is that little ones's body still hasn't matured (duh, that's why they're still little, lol) and that includes their internal thermostat. They have a harder time regulating their own body temperature. So sticking them in a too cold pool, or even just outside without the proper attire on a cooler day, can be hard on them. They may not shiver as quickly as you would even when they are cold, because their system isn't mature yet.
If he was shivering AT ALL he should have immediately been put in dry clothes and warmed up. The water may have FELT warmer to your husband, but was there a thermometer that gave the actual water temp? Too much below normal body temperature will cause a small child to rapidly(!) loose body temperature. Even 75 degree water can be rather chilly. That's 23 degrees below normal body temp. That is what the coastal waters around here are right now. I wouldn't be out swimming in it.