Halflings should not be blocked to enter a blocked door for example if the door is blocked by a creature or another character that has legs that the halfling can move through.
Just how small are the halflings in your game!?
Remember that, certainly in combat, those legs are going to be moving all over the place. If I were trying to position for an arrow shot or to dodge a sword swing, I'd be less than impressed if I tripped over an impatient halfling.
