One child is a tattle tale..

I would explain to him that there is a time and a place to tell and when there is a time and place to not worry about something. When he is about to run up to you and tell ask him before he says anything if it is important. If he says " Yes" then let him. If then it isn't explain to him why it is not important, and give him an example of when something would had been important through his example.

Tell him he is only responsible for what is going on with him. Tell him he does not need to run and tell you about everything the others do and that no one likes a tattle teller. Tell him that there are major offenses and minor ones and unless you ask him who is responsible for something he need not tell you about minor ones. Tell him it is important to have a good relationship with his siblings. You should also tell the instigators not to gang up and pick on him but to set an example and help him learn and grow.