The rule is clear. The accompanying pax must be at least 18 yo.

To the OP. I think there’s more than $0 value, but agree that there’s less than $300. Specifically, if the flight is diverted, DL will take a greater degree of responsibility and not strand your kids.

Last summer my 17-yo kids were scheduled HND-(JL)DFW -ATL (DL) and crowdstrike happened. No hotel would give them a room and I had to get them alternate transportation, which happened to be on WN from LUV and an Uber. Meanwhile, I had flown via ORD and had my own DL issues.

All this to say, stuff does go sideways and this is a type of insurance to mitigate the issues.