The Palo Alto Library parenting program refuses entry to parents mistakenly bringing babies or children. Some preschools specify that their tours are for adults only. And toddlers are not always welcomed trick-or-treaters.
On the flip side, I'm amazed by my doctor's office who (happily) accommodated my son when I had to schedule an immediate appointment but I wasn't sure if I could find a babysitter in time. And semi-fancy restaurants with staff who not only invite us to dine in, but interact with our son, provide kid menus, high chairs and covered cups.
What venues did you misread as either family- or not-family friendly?