Let's face it, 'tattletales' aren't always the most popular children in school by their peers (or their teachers). Being a leader and a rule follower is a good thing; however, there are times when the 'tattletale' child will become the kid that gets involved in everyone else's business and seems to bring problems to the surface that may have worked out on their own. They may seem helpful at times but other times they create more problems.
How do you teach the tattletale child to be helpful but not bossy or rude? Sometimes, these children can be dependable and have a positive influence. You can trust them to do what they are told and if there's a dangerous situation, you know they will step up and look for help. The problem with this is that these children will often get consumed by care-taking and taking on other children's worries (or even the adult worries) instead of being a child and playing normally. This can create social problems because peers may not trust their intentions or feel inferior when playing with this child.
Toddlers often go through a phase of being a tattle tale while they are learning right from wrong but they quickly grow out of this phase when they start to learn when it's acceptable to tell an adult and when they should keep to themselves. This is simply a matter of social development. As children get older, they start learning to focus on their own activities and challenges and begin to solve their problems without needing as much adult direction.
It's important that we remind ourselves that these children may be looking for attention from us and tattle tailing may be their way of feeling good about themselves. If they are "supervising" too much and telling you what other children are doing wrong, say to them "thank you very much, but that is not your worry", and try to give them attention in other ways. Help them to see that they can get your attention without being the "teacher".