Rectangled Babysitter

A rectangular device, most commonly a smartphone or an iPad, that is given to young children to keep them occupied so they don't annoy their parents while they drink.

"Come down to the pub and have a few beers?"
"Nah I can't, I'm looking after the young fella."
"Just bring him and down with the Rectangled Babysitter."
"Genius, see you in 20".