Simply repeat back the words. Don't worry about sounding like a parrot. That is unimportant for now. When you do speak up, be sure to use open responses and not closed ones. Closed responses give advise, put down, or ignore the feelings of the child.
Open responses indicate that the listener has heard the feelings behind the words.
This is a little more difficult and may require some practice. Open responses don't mean you agree or condone your child's word. They simply communicate that you are listening. Other healthy communications include monitoring your tone of voice and body movements. Your nonverbal communication is as important, maybe more so, than your verbal communication.