I am on the side of competing in those spring sports. First, the workouts and competition will be good for their introductory phase by keeping them in top shape. Second, the teams and coaches are counting on them. Third, while injuries can happen in any sport, its not like they won't have time to heal. Fourth, let 'em go out with a flourish.
I get the "bubble wrap" psychology but to me that means avoid high risk situations. In both cases mentioned above we are talking about track & field. All-in-all, not a high risk sport. I have been around track my whole life as an athlete and a parent. I have two kids who were state level sprinters (and hurdles) and another two who threw discus all four years. Sure, there were shin splints, muscle strains, face plants, rolled ankles, etc - but nothing that would cause me to recommend sitting out their senior season.