Buy happy meal, secure child, call authorities. Also, look for new job- I like to imagine my work ethic is such that if I were on such dire straights with a manager, it would be becuase they are a douche and I shouldn't be working for them.
Personally, I like the situation my district manager brought up at a meeting the other day: 'you are a manager in a small retail store. A woman comes in pushing her elderly mother in a wheelchair. it quickly becomes apparent the woman is... 'challenged', and shouldn't be out by herself taking care of an invalid. They go toward a back aisle, where the woman suddenly strips naked and stands there, dazed and oblivious to the world. What do you do?'
This wasn't a hypothetical, by the way... it happened a few weeks ago in another store in our district, and since we were in a manager meeting, she was curious how we would have handled it. The store in question blocked off the back aisles, got the woman's husband's phone number from the mother, and had him come in ad snap her out of it.