I agree 100%!! I am part of the family collection because we cater well to babies and young children, we provide toys, crib, baby bath, high chair, beach toys. I have done this since 2015 when infants used to pay like everyone else.
The no charge for infants under 2 is not good for me because as you say they are so messy and families with infants under 2 often leave the apartment messier than any other guests! I am NOT happy about this, AIRBNB needs to change it! My cleaning fee is the same as for all other guests. When infants were paying guests, the extra time cleaning/broken items were covered by their paying rate.. now I am left in the lurch. It's not fair that I should be adding a separate fee with this model for infants under 2 in the description! This would make families feel discriminated against and that's not fair on me as a host or them as a guest!