@Dave1011 It isn't the same type of discrimination as declining to host someone because of their race, sexual persuation, nationality, etc. at all.
Children have different needs than adults do, and there are different levels of safety needed with children in a home. Adults don't need baby gates on the stairs so they don't tumble down them. Adults don't need unbreakable plates because they think it's fun to throw them off the table. Adults don't require baby-proof covers on electrical outlets to prevent them from sticking something in there and getting electrocuted or safety latches on cupboards to prevent them from drinking the cleaning fluid stored there. If you are a parent, you are aware of this. It's not all about sticky handprints on the wall.
And no, most Airbnb hosts aren't at all like hoteliers. We don't provide daily maid service, or 24 hour desk reception, we don't have a secuity staff to deal with unruly guests. We don't provide a mini bar. We are just renting a homey space, perhaps a private bedroom in our homes, a converted garage on the property, a vacation home we use ourselves, etc. Of course now there are property-managers with hundreds of listings for places that are exclusively used as Airbnbs, and it could be argued that they are more like hoteliers, but the traditional -type Airbnbs are not.
There are plenty of Airbnb that cater to families, so that some don't accept children shouldn't be some big deal.
I raised three and have 6 grandkids. I like children just fine. But I also acknowledge and understand that not all Airbnbs are suitable for them, and respect a host's choice to only rent to adults.