why is playgroup so exhausting?

really....it mostly involves sitting around and talking to other mums for 2 hours whilst keeping an eye on a bunch of overenergetic children (in the case of our playgroup mostly boys). So why am I exhausted at the end of the session??? Finally after about 2yrs of playgroup I have worked it out....it isn't the actual playgroup that is exhausting....it is extracting the kids from the playgroup and getting all three of them strapped into the car ready to go home that wears me out!