Did I miss the memo here? Did Airbnb ask hosts about this decision?
Okay, I get it that people with infants usually bring portable beds, but once they're up and running, my inclination would be to charge extra rather than not charge for toddlers. Up to a year, sure.
We're absentee hosts, but our friend who does our turnovers and reports how people left our cabin often reports having to do extra cleanup, cope with quantities of disposable diapers, etc. And it's totally easy to understand how a mom with teeny-tinies is hard pressed to be out at checkout time, much less tidy up the dishes and mop the squashed blueberries off the floor, and the cupboards, and the furniture...
Fortunately, our accountant recently advised us that our property, on a main road and unfenced on one side, simply isn't appropriate for kids under 6, so we have changed our policy and rent only to adults and people with older children. But I think Airbnb is imposing on hosts with this one, and I'd suggest re-thinking it.