Quite a few marathons don't let you, but those that do have people and I'm sure it's possible.
I've not raced more than 6km with the Baby Jogger Performance, but it rolls so well on tarmac that if I was in marathon shape I'm pretty sure I could do it - would also be good as you can carry a drink (get a water bottle holder for it), food, anything you might need without being weighed down!
I add less than 10% to my time with it over 5km, so not a huge amount of difference in the marathon on time hopefully.
The question really is the baby - with bricks I'd be very happy, with DD now I think she gets a bit bored after 90 minutes, even with lots of other runners to say "well done" and things to see. 3.5 hours+ is a pretty long time to be sitting around.
So I've just bought a second hand Baby Jogger Performance and am loving getting back into running again and taking dd with me. I was running today and thinking "would it be totally bonkers/impossible" for me and her to do a marathon together....
Has anyone ever done this and if so, how did it work logistically with lo being in the pushchair for all that time and needing to stop to feed/change/stretch etc?
I obviously wouldn't be looking for a time, but would it be impossible in any case?