The parent of an underage player doesn't have to play, they just need to remain close enough (20 to 40 feet) to the underage player to supervise them and maintain their own comfort level of the risks their child takes.
While parents can wander around the forest following their child or encouraging them, the parent may find participating more fun. Since people on the field exist "outside" of the official game space, they are prohibited from pointing out enemies or giving specific instructions.
Experienced admins and field marshals have scope to coach players without participating. This kind of behaviour also excludes pointing out enemies or giving specific instructions. Usually coaching consists of convincing the player to get closer, move faster, or use particular techniques; essentially reminding the player of things they should already be doing.
So the parent may find participating as the
fire buddy to their underage player a better option than just hanging around in the forest.