I just read a great little article by Julie Lowe on how to respond when children say, "I don't know." (E.g., "Why did you hit your sister in the face with that pool noodle?"). Here's the closing paragraph: 

As adults, parents, teachers, leaders and counselors, we can become much more winsome and patient when asking kids questions, especially in response to “I don’t know.” Do the hard work of drawing kids out. There may be times when you allow them to walk away from the conversation to consider things, but give a time frame to show the discussion is not over and then follow up with them. They may challenge you, reject you, or be angered by your attempts, but you will model care by your persistence. We do not always get the privilege of seeing the ways in which it speaks of our love for them but Galatians 6:9 encourages us. “Let us not become weary in doing good, for at the proper time we will reap a harvest if we do not give up.”

I'd encourage you all to dig into the CCEF website. I found this post because I subscribe to their email newsletter.