This one was in the Big Book of Urban Legends I had:
Couple is waiting on babysitter to take care of their infant while they're on vacation. Babysitter is late and the couple is worried they'll miss their flight. Babysitter calls to say she's leaving now and will be there shortly. Couple decide to leave to make their plane. Babysitter is in fatal car accident. Couple returns to find their rotting baby still in the high chair.