It's not against the law in Florida so it is probably up to the particular restaurant. for it to be Disney-wide it would have been Disney's rule. I have not heard of it happening at more than one restaurant, maybe two, so it is probably an individual thing.
Rose & Crown does not have at the bar seating, you stand there. They have a few chairs opposite the bar. They have no rules as to who can sit there. when they are expecting to be very busy, they take out the chairs and don't let anybody hang around, they have some CMs waiting to usher you out when you get your drink. Nothing to do with whether there are kids in the party or not.
I have no idea what sites the OP is talking about, or where those sites get their information.