In a medium-sized mixing bowl, combine hamburger, milk, onion soup mix, and Worcestershire sauce. Roll the mixture into small balls. Arrange meatballs on a cookie sheet. Broil for 10 minutes, or until cooked through.
In a small bowl, mix ketchup and brown sugar. Transfer mixture to a slow cooker. Add the meatballs to the slow cooker.
Cook meatballs on high for approximately 30 minutes.