This is a really interesting topic!

The policy of not seating people with small children on the same flight in the exit row makes a lot of sense in theory. It would be natural for OP’s wife to be more focused on their child a few rows ahead than on helping random strangers evacuate. Worst case they’d at least be distracted.
BUT then that opens a can of worms like do we need to make sure everyone in the exit row is traveling alone and doesn’t have a significant other, grandkid, close friend, parent, etc on the plane that would affect their focus in the event of an emergency?

sorry for the ramble, just surprised I’ve never thought about this before.