So, you're producing a project that features some kids in some key roles. You spend a small fortune developing the project. You hold auditions, and eventually find the perfect kids to star in the piece. So, you sign them to written employment agreements, and everything is looking terrific and you proceed into production.
You're halfway through the production process when one of the kids decides she's not having fun, so she's quitting. Your project is completely off the rails, both creatively and from a business perspective. Sure, you can start over… recast the role, hope that the project can be salvaged, and you won't have lost everything you've invested.
“But wait” you say. “She signed a contract! She can't just quit. I'll sue her for damages.”