Falling out of the bunk bed and damaging the floor.

Wow that is one hard head.

Never had this problem, but I don't think expanding foam would hold up. You may be able to inject some bondo into the depression. It's self curing but you would need to drill at least a 1/4 in hole through the laminate to get a big enough syringe to flow the bondo. Might have to do it in a couple of layers to make sure it fills the cavity properly.