It was at a pace he could cope with, and a speed he dictated with plenty of of water and rest stops. his normal runs are around the 10 mile mark which I think is about right for his age (10), this is a once a year thing really.
Incidentally after the marathon (and 30mins rest) he wanted to cycle home (another 3 miles) so we did, another hour rest and he ran off to the park to play on his bmx.