Kids mode will allow children to use their Apple Watch for activity tracking, and parents will be able to manage their children's devices, according to code spotted in an early version of iOS 14 by 9to5Mac. From what we can tell, when enabled, Kids Mode will serve up an Activity Ring on an Apple Watch with labels and goals that are different from what an adult would normally see on their watch.
Adults see Activity Rings for active calories burned (red), minutes exercised (green), and hours with standing movement (blue), but an Apple Watch set to Kids Mode will not highlight the number of calories burned. Instead, it will track move time with exercise time and hours spent with some stand activity. So, children might see a movement goal of 60 minutes versus 300 calories burned.
The idea here, obviously, is to keep young ones focused on being active and healthy overall, versus calorie restricting to lose weight. 9to5Mac also suggested this Kids Mode will work with new parental controls so guardians can restrict certain Apple Watch features during schooltime.
Presumably, Kids Mode will be available to all Apple Watch models set to run watchOS 7, and not just the next-generation Apple Watch, but that hasn't been confirmed by Apple yet of course.