I'm with Krystal on this one.  I think the "yay" is probably a teen or adult happy with their result on the scale. I love it. 

But I'm also with you and Moonlyght on the quick check on the kids whenever I hear giggling. I have no idea why drawing on the wall annoys me... but it does.  I'm gonna have to go with my daughter who said, "I 
just fixed that wall!" as she scolded a child.  (That, of course, caused me to fall out in laughter because I could remember saying similar things to her soooo many many times when she was younger.)  Anyway, I'll use that as my excuse for scolding the children who do it. 

  But the dirt, I let them have at it.  The giggling is nice to hear and my grandfather used to say that a child has to eat a pound of dirt before they are four years old or they just won't grow right! 
