Hypothetic Situation: What would you do if you saw this?

You are in a bookstore, just browsing, shopping or whatever.
Meanwhile, a mother is checking out at the cashier, has a toddler with her. She has to sign the receipt, so she puts her toddler down. He walks away, but still within eyesight, so she looks down and signs the slip, looks back and her toddler is gone.
She runs over to the door, he couldn’t possibly have gotten out.
She begans yelling her sons name, and running up and down the aisles.

Do you just watch? Do you try to help?

I’m asking what you would do. No judgement of the mother, even though I’m sure everyone has an opinion ;)