I don't think this would be a problem, but you'd have to be damn sure who's picking up the kid. Maybe take pictures of the kid with their parents and confirm once they come back to pick them up. Keep like a safe word that only the babysitter and the parents would know. THis is also good if the parents allow someone else to pick up their child.
"What's the password for Johnjohn?"
"Banana".
"Proceed".
Or a "Lost Password" question line. Fill out forms. Protect the kids and the babysitters for sure.
My informal CPR training through my highschool showed how to take care of children. Had my baby been choking, the whack I gave it would have dislodged the block and a lung. I really smacked that poor thing ^^; Thank god it was fake.