Love it! My fiancé signed up this morning and spread the word on FB. I've been thinking about this for awhile now, but in a marketplace form.
Have you decided how to monotize it? One thought I've had would be the Airbnb model, but given that it's way more niche than finding a place to stay for vacation, I think this would have to be tested with an audience who is in dire need of this. Maybe find a way to target the "babysitter" audience?
Looking forward to seeing how this progresses nonetheless! Best of luck.