The leader probably should have stayed but I don't consider it a serious error since he was following a road and could easily return. And, we don't know the qualifications of the two adults that stayed with the kids. But yeah, leaders need to lead - stay with the kids and send another adult down the road.

It is neither difficult nor unusual to get lost on such hikes. You can't develop plans or preparations so elaborate that it won't happen: even GPS & maps can lead you astray (maps are wrong sometimes, even aerial photos out-of-date and deceptive...)

You always have to have Plan A, Plan B and Plan C, and invest in each based on the consequence of having to fall back to the next plan and the likelihood that all predecessor plans fail. You put effort into "don't get lost" as Plan A, but not to the point of neglecting Plan B (extra rations, etc) and Plan C.

Overall it's a good lesson in contingency planning for the kids. It would be interesting to know what Plan C(?) was since they were likely nearly out of food at that point.