If You Anticipated It, Then...

Two boys and their father came into the store. The boys were both eating ice cream. I intercepted them and told them that we didn't allow food in the store, so they'd have to finish outside.

The boys dutifully turned around and left. Before following them, their father said to me, "Sorry. They half-anticipated that."

First of all, they should have fully anticipated that, since there's a sign on the door saying "No Food or Drink".

Secondly, if they were "half-anticipating" it, why didn't they look at the door to see if there was a sign?

Finally, "half-anticipating" means they knew they shouldn't bring the ice cream in. So why did they bring it into the store?!?!?