British Orienteering Rules 2007
1.1.3 Competitors take part singly and independently, unless entered as pairs or groups in competitions that permit such entry.
...
7.2.3 Competitors shall not collaborate in any way unless members of a pair or group competing together.
So what should I do when a junior comes up to me in the forest and asks for help? This seems to be happening more and more recently, to the point where it's not unusual to be approached by lost children twice at the same event. I don't mind stopping to show them where they are - at the speed I generally move, twenty seconds either way makes little difference - but I always wonder whether it's fair on the kids who do manage to get round on their own.
This is particularly true on the "higher" junior courses: I think it'd be a bit cruel not to help a lost W10 running Yellow, but at a regional event in the last couple of months I was asked for help by a kid running JM5S (at a guess, I would say he was 13ish) - should he have been able to sort himself out? I was also faintly relieved that nobody came up to me at the YBT first round... At the same time, it can be very hard to say "no" to/ignore a lost child. (Much the same applies to lost adults (not always novices), though here I'm (in most cases) less willing to help on the grounds that they'll probably beat me anyway

I suppose in an ideal world the kid would declare themselves n/c at download, but I think that might be a tad optimistic.