Serious Face

It was time to leave the park and, as usual, neither girl wanted to leave.  So, I had to put on my 'I'm serious' face when saying "Come on Gwen.  Let's Go.  Now".   Gwen looked up, saw my 'You'd better listen' expression, made this face in return (which is an impression of my serious face but with a smile) and turned back to playing in the sand.  I think I need a more intimidating expression.