Talking and listening helps.
This is a fact!
Talk to your children about favoritism in a calm manner, at a time when there are no struggles actively on the front burner. Try something like “Joanne, a couple of days ago you mentioned that you think I love Alex more than you, and that I let him off the hook too easily. What makes you think that I love him more?”
Think carefully about your child’s answer to determine whether there may be a grain of truth in what she is feeling.