I don;t think this is affordability
As I said earlier, they have to pay a child's fare after the age of 2 anyway. Do people suddenly become rich enough to pay for their child's seat after two years?
It is customer expectation, and the FAA or CAA should simply mandate that airlines cannot allow children to sit on the lap of the parent and this would put all airlines in an equal competitive position.
Apart from the horror of having unrestrained infants flying about the cabin, the report also suggests two mothers became totally detached from their infants. This raises the possibility that they will impede evacuation in a panicked effort to locate their child, other passengers re-entering the plane in an effort to rescue the child (as happened at Sioux City), etc. It is a nightmare and simply cannot be safe for the infant or for the other passengers and places the CC in an impossible situation.