You are correct that there are restrooms there. However besides servicing the needs of visitors to Fantasyland, there is another reason for restrooms by the Fantasyland/Libert Square border. There were no flushing toilets in the late 1700’s, which is what Liberty Square is modeled after. Therefore, if you have to use the bathroom when you are in Liberty Square you aren't able to, because Disney kept with the them and there aren’t any there. You have to go either to Fantasyland (currently by Peter Pan) or over to Adventureland. Even the bathrooms in Liberty Tree Tavern are in the back of the restaurant, that is technically over in Adventureland. So the bathrooms (currently by Peter Pan) are there to obsetnsible handle the needs of the Liberty Square area in addition to providing use to the many people that flock to Fantasyland.