by default, Airbnb doesn't charge for infants (0-2 y.o.), and children 2-12 y.o. are charged as adults. There is no option for the range 0-4 y.o.
So, to make your life easier you could just go with a flow and charge 2-12 y.o.
In case your guests book for 2 adults and show up with kids you can make them accept the change of their reservation on arrival. If they don't agree you are not obligated to let them in.
A good practice would be to ask each group of guests to confirm how many of them are coming.