Is it so hard to know that by excluding the baby you exclude your friend?
This has been said, over said, been a common theme.
Noone should assume they can separate, or indeed ahould separate a mother and baby.
You alienate mothers.
If thats your choice that's your choice, but it would be unreasonable to think it a reasonable thing to do to a friend.
Of course, you can, and people do, for all sorts of reasons, but that doesn't mean its fair, reasonable or a kind way to treat someone who's suposed to be your friend 
Choosing a child free space when you are fully aware that a good friend has a new baby is actively choosing to exclude the friend.
All other forms of blanket exclusion are rightly called out as discriminatory, you couldn't exclude any other class of person.
All these places allow animals where needed.
Parents of older dc can make choices about having their dc around, and reasonable to want adult only experiences, but this isn't a choice for a new dm, and it shouldnt have to be.
God you would think babies were devil spawn or something!