1. Cook tortellini according to package directions. Meanwhile, in a 3-quart saucepan, bring broth to a boil over high heat.
2. Add tortellini, watercress, and scallions to broth; simmer over medium-high heat for 2 minutes. Serve garnished with Parmesan cheese.
How kids can help: Older kids can chop the scallions; younger ones can sprinkle the Parmesan cheese over the soup.