I'm TIRED Of My Sister Dumping Her Kids On Me Without Warning And I Need Advice

Odds are, at some point during this exchange your sister will ask what you’re doing, and why. And THAT my friend, is what you want. Now SHE has started the conversation, and you have to tell her very clearly, and very calmly that you weren’t asked to babysit today, therefore, if the girls are causing trouble or look like they’re going to hurt themselves in front of you, this is what will happen.

Now, I know people will disagree with me on this, but you have to correct this habit in this way, because she needs to understand in real-time how her actions effect other people at family events.