How do you end tattling?
Tattling is telling on someone with the purpose of getting that other person in trouble. This is different from reporting. Reporting is when someone sees that something happening needs adult attention, or someone will end up hurt.
I encourage reporting. I also make sure my children know the difference between the two. When I had foster children, there were times when I was really glad that there was another youth around to report things about the other youth that needed my attention.
Reporting is good! Praise it and ask for it. Tattling is bad because is puts one family member against another.
First, realize that most children believe telling on someone helps you parent, helps someone else make a good choice, helps themselves look good in your eyes, or helps them get something they want.
Since this is the reason they're tattling, then you should acknowledge their good intentions first. Here are some things you can say:
Thank you for trying to help in this situation. However, when you come to me just to tell on someone else, I worry just as much about you as I do about your sister.
I worry about your sister, because I think that she might not feel very loved when people are trying to get her in trouble — instead of being her friend and motivating her to clean up her room.
I worry about you because I feel like you're worried about something and don’t know how to solve it, except to get someone else in trouble.
What you should have done when you noticed that your sister didn’t clean up her room when asked was ask yourself if this is any of your business, and then ask yourself if she is hurt or could get hurt from not cleaning her room? Could anyone else get hurt from her not cleaning her room? If the answer is "Yes," then you should tell an adult, because we don’t want any of our children to get hurt. If the answer is "No," then you should do nothing, because we want our children to make their own choices and earn their own consequences, so that they can learn and grow. The other option is to gently remind your sister that it's almost time for rooms to be clean, and that if she doesn't then she could earn a negative consequence. This kind of reminder would be the most loving option, if your sister is open to reminders.
Do a pre-teach and share what consequence will be earned if he still chooses to tell on his sister with the intent to get her in trouble.