Yes. I have seen people in shorts and flip flops turned away. I have seen people wearing ball caps asked to remove them.
and I saw one lady who was wearing a very revealing top that was really meant to be a beach cover up turned away.
The smart casual dress code allows jeans. It asks that there be no shorts, beachwear, sleeveless T-shirts on men, it isn’t that hard to abide by.
your teens might be happier eating in the buffet. They won’t be alone.