Acknowledge Tattling

Okay, before I start into this let me begin with I AM NOT PERFECT!  I used to try and squish out tattling in my classroom with Tattle Trees and items of the like that students told problems to.  What I'm about to go into is why I don't do that anymore.
Around the age of three-five children are beginning to lose so much of their egocentric focus and begin looking at what other people are doing.  They know by know what the expectations are for them from you so when they see something that does not fall into those expectations, they feel the need to share this with you.  
To quote ABCmouse.com "Advisor Tip: Learning something new is exciting to a child. When your child shares a new fact or asks questions about a recent topic of study, acknowledge and praise the enthusiasm. Take the time to discuss what your child finds interesting. Positive and encouraging language will empower your child to learn more and will create a positive attitude towards learning."  
What many people identify as the "tattling" that they don't want to hear are things that your child feel is important to share with you. Take the time to thank them for sharing information with you and also take the time to explain why that behavior might be okay so that they don't feel the need to "tattle" next time. When they "tattle" they are sharing something that they feel could be important.
It is difficult for young children to realize the difference between tattling and sharing something important because to them, it is all important.  They feel that this is something important enough to come to you and discuss.  We sometimes feel as teachers and parents that children are purposefully trying to get another child in trouble with tattling.  This is not always the case.  They just want their information to be shared, acknowledged, and learn how to cope with this new information.
While, yes, I might still hear the occasional "I'm going to go tell Ms. Megan!" Which I don't see so much as tattling but as attempts to get someone in trouble.  When I hear this simple phrase yelled across the room, I will wait until our little birdie flies her way to me, sit down to her level, and discuss with her about what she felt was wrong that she needed to share with me and that she couldn't tell the person how to fix their behavior.  I like for my students to be able to build the skills to self-correct but also to be considerate enough to help nudge a wanderer back on the right path.
The best way to break "tattling" is just by talking about why the behaviors they are sharing with you are alright or help walk them through problem-solving strategies to be better prepared to handle the situation independently next time.  In my years, I have heard "tattling" stories of all kinds from the every popular "HE'S NOT SHARING!" to the unusual "She won't let me put the crayon in my nose!"  Look, if that last one isn't a clear demonstration that this child obviously needs just a few minutes of discussion and guidance, I don't know what else would.
Two things that hurt more than help tattling: ignoring and assuming.  While the ever popular "if you aren't broken or bleeding" is great once children have a firmer grasp on the idea that everyone's a little different, at the beginning of this phase it isn't very helpful.  Again, these children are in the middle of new learning opportunities when they come to share this information (even if it has a whining sound to it).  Just take a few moments to help them learn.  You'll find that they won't be running back to you in five minutes to tell you the same thing because now they know!  Now it makes sense why Sally won't let you put rocks in your ears.  She's trying to make sure I don't have to go to the hospital to get those things out!
Assuming breaks my heart.  Assuming happens when teachers or parents just assume that whatever this three to five year old has just said is true.  Not saying it isn't, but sometimes they don't know exactly how to phrase or might not be fully aware of situations before they tell.  Let's say, my daughter knows that she isn't allowed to watch certain programs but she walks into her friend's room for a playdate and she's watching the forbidden cartoon!  She might run and say "Bessy's watching something she's not supposed to!"  An adult who assumes would then proceed to have Bessy in trouble even though Bessy did nothing incorrect by the rules of her household.  That's a learning moment more for my daughter to say "I know we don't watch that in our house, but Bessy's parents said that's okay for her."  Now she knows.  Now I won't hear anything about it in two seconds when my daughter runs back in and Bessy's still watching it.  That's part of learning that we're all different.  Not only might we all look a little different, but we all behave a little differently too.
Well, what about the children who lie to get other children in trouble?  That's a whole different seed there baby.  Again, not tattling.  That's lying.  Having the little girl from the reading area to come crying about how Bobby (who's been in blocks for the last 20 minutes) just stepped on her fingers.  Okay, this one actually requires something absolutely mind-blowing for this.  Are you ready?  OBSERVATION!  Seriously, if you're paying attention and watching the children under your care (be you parent, nanny, or teacher.. DOESN'T MATTER) then you will know that Bessy's doing one of two things; lying or telling you something from four weeks ago.  I kid you not, I've actually had a student two hours into the school day have a breakdown because of something his brother said at breakfast that morning.  In observing, you'll be able to address your little miss on lying or helping her to cope with the fact that while yes, Bobby stepped on her fingers four weeks ago and you're sorry that this still has her upset.
Oh, and number one reason I don't like to deny communications like this with younger children is that I want them to feel that they can openly communicate anything with me.  When they run to me to tell me these things, they're telling me that they trust me.  They trust me to provide them with help and answers to things that they cannot understand.  They feel that they can come and talk to me without judgement.  Especially with my daughter, who I want to be able to come and talk openly about things that might bother, upset, or confuse her thus keeping the lines of communication open helps me to better know and understand what is going on in my child's life.

But again, we're all a little different.  No one says you have to live or teach like I do.  I'm Telling! has a wonderful breakdown on what commonly motivates children to "tattle".