Marissa Picard/WMG

The Field Trip was really a Holodeck Simulation preformed by members of the Enterprise.
Hence why the kids acted like adults and followed Marissa's orders, because they really aren't kids, but officers who are just simulating what would happen had a ship crashed on a deserted planet. This also explains why Picard was not so awkward around the kids, because they weren't kids. The Kobayashi Maru test was just the officers saying "screw it" and deciding to return to a basic, unwinnable scenario. Hence why the abrupt end.