Having trouble explaining sin to your kids? It may help to be confident that you understand sin yourself. Sin is not a behavior. Sin is not an attitude. Sin is not even a choice. Sin is in our very nature. It's in the fabric of who we are. Has your 13-month-old ever hit you out of anger even though you're certain they've never witnessed someone act like that before? It's because it is ingrained in them. Has your 2-year-old ever said something so catty and out of character, and you've tried and tried to figure out where exactly they learned that phrase? No one had to teach them - it's part of who they are. Despite our very best efforts, our daily prayer, surrounding ourselves with wholesome influences, and limiting exposure to harmful things, we cannot help but be sinful. It's part of our make-up - just like our eye color, heart rhythm, and shoe size. Because of the original Fall, sin nature is beyond our control.
So, how do we explain that to our kids without giving them an excuse to misbehave?
When I taught chapel, I used a visual to teach sin. Of course this topic is way more complex than this visual will allow. But it worked as an introduction and a conversation-starter. It helped to show that our nature is sinful, that we will continue to sin even with Christ in our lives, and that Jesus gives us tools we need to deal with our sinful hearts.
First, print a copy of the Sinful Heart and the Fruits of the Spirit. You can color them, have your kids decorate them, or just leave them black-and-white. Cut out the Heart and all of the rectangles.
Each rectangle represents a sinful thought or behavior. I provided plenty of blank ones to fill in with something appropriate and relatable for your child. Using an Exacto knife, cut along the top, left side, and bottom of the door. Fold it back along the "hinge" to create a door that swings open and closed.
Flip it over, and cut a triangle out of another piece of paper to tape on the back to make a pocket just like the grey triangle below. Tape only along the right and left sides leaving the top open.

Turn it back over, open the door, and fill it with the rectangles representing sin.
Now you're ready to get started. I think it may be helpful for me to provide a basic script that you can either read as you present this heart or use as a starting point for your lesson:
"Do you see this heart? This heart is just like ours. Want to see what's inside? Open the door. Wow! It's filled with lots of things. [Read a handful of the rectangles.] Gosh, those don't sound good at all. Did you know that we have things like this in our heart? In our Bible story, we talked about how Eve made a choice that went against what God told them. When Eve made that choice, sin entered our hearts. From then on, everyone is born with yucky sin. Sin is anything that sets us apart from God. It can be bad choices we make, mean things we say, or even things we think about. Sin is a part of us that we cannot get rid of on our own no matter how much we want to. God is holy and perfect, but we are not. God hates sin and cannot be near sin. So we cannot be near Him unless we can clean this sin out of our hearts. Since we can't do that, and since God loves us so, so much, He came up with a very special plan. He sent Jesus to clean out our hearts for us. The Bible tells us that Jesus stands at our heart's door and knocks quietly. He waits until we ask Him in to help us get rid of our awful sin. When we invite Him in, He gets to work right away getting rid of our sin. [At this point, have your child pretend to clean the heart with a wash cloth, and remove all of the sin rectangles together. Close the door, but secretly put a couple more of the sin rectangles back into the pocket.] The problem is that, since sin is a part of us, it just keeps coming back. [Open the door to reveal more sin.] But, since we've opened the door to Jesus, He promises to keep checking around and getting rid of our sin every single time it comes back forever and ever and ever. He will never leave us once we have invited Him in. So that means that every sin that has ever been in our heart and every sin that will come into our heart forever is already taken care of. Isn't that so amazing?" But, there's even more. The Bible tells us that Jesus wants to help us with special tools to do our best to keep the yucky sin out of our hearts. When Jesus is in our hearts, He brings the fruits of the spirit. [Place each of the fruits of the spirit into the heart pocket explaining each as you go.] These fruits wlil help us to act and think in a way that is pleasing to God. When a friend takes a toy away from us, we have been given self control to help us to not hit or push or grab the toy back roughly. When our moms and dads cannot help us right away, He has given us patience to help us to wait without whining or throwing a fit. So we not only have Jesus to clean up our sin right away, but we have been given special powers to keep us from sinning too! God is so, so good."
I hope you and your family find this illustration helpful. I am praying over this post (which, by the way has been the most technically-challenging blog I have ever written - literally everything has gone wrong, so clearly this is an important message) - that it would touch lives and hearts as you explain the absolute most important message we can share with our kids. Please feel free to contact me with any questions at all along the way. I do not know all of the answers, but I would love to learn and search alongside you.
Happy teaching!!