Use an "I-statement".
Starting a conversation talking about yourself prevents your child/partner/loved one from entering the conversation on the defence. It sets the precedent that the conversation isn't about them, it is about your interpretation of them.
2. Approach with curiosity
When you centre a conversation around, "what is going on here that I am missing? How do we work through this?" rather than "this is annoying me, why are you like this?". The dynamic is now one of problem-solving rather and a name and shame exchange. It's both you, the other person, and the issue you are facing rather than you versus them.