This guy on Reddit's /r/running claims he ran a sub-18 with a stroller and 2 kids in it last Saturday:
http://www.reddit.com/r/running/comments/1elyme/i_won_a_5k_this_morning_while_pushing_a_stroller/
I'm kinda skeptical. He says he usually averages 5:20 per mile in the 5k. Doesn't seem to me like 5:20 would convert to 5:47 when you have a stroller and 2 kids. Thoughts?