Haha...thanks for the morning laugh. I agree it is crazy to not charge for one of the messiest ages. Because so many parents are going to claim their 2 year old is under the age of 2 and qualifies as infant. So we will have kids at 35 months being called infants!
Anyway, I would not be surprised if Air's goal is to increase the age down the road...to maybe something like 5 and under stay free. It is not a good experience for the traveler to submit a booking request and then be denied because their group is bigger than the max guest count. Air could choose to allow hosts to allow kids for free, or to charge different rates based on different ages. It's the same with pets. Hosts should not have put in a house rules section the fees for children and pets. It seems they are only allowing hosts to note in their house rules for now, as they want to make it all free in the future.
But trying to force hosts to allow more than their max will be problems, as some areas do not allow more than a certain occupancy or you are violating fire codes.
Air will reverse this BS only if enough hosts tell guests they need to cancel for violating max occupancy.