FUBAR
Footballguy
This is the answer for us.
Our oldest turns 13 in a couple weeks and has watched his brothers for a few hours at times this past year (including a now 5 year old). We got him a phone before we left him more than 15 minutes as we don't have a home phone.
I've left his 11 year old brother with the other two a couple times to run to the store when my oldest wanted to join me.