I came up with this object lesson(s) that I thought I would share for future reference. This is very visually stimulating, so be prepared!

You will need:

10 books
masking tape
pepper
dish soap
bowl of water
bowl of crushed crackers
bowl of water based paint
bowl of syrup
bowl of dirt
bucket of water
cup of dark cola
3 buttons

First explain the six steps of repentance:

1- Know you did it
2- Feel sorry
3- Confess
4- Ask forgiveness
5- Make wrong right
6- Never do it again

First lesson-

Put a strip of masking tape on floor.  Have a child stretch out arms and walk the line (should be really easy).  Then as each pass on the line, add a book or two to each hand. It gets harder and harder until they start dropping books..... Relate to repentance and sin.

Second lesson-

Place a bowl of water where everyone can see it.  Put pepper in it (represents sin).  When you repent- drop a tad bit of dish soap in the water - the pepper goes away.  Dish soap represents forgiveness.  Again, relate how you want.

Third lesson-

You will need:  bowl of paint, bowl of syrup, bowl of crackers, bowl of dirt, bucket of water. 

Get a volunteer or do it yourself.  Put hand in paint, you are dirty from sin.  If you don't repent, you keep getting dirtier and dirtier. Put hand in syrup, then in crackers, then in dirt. You are covered in sin. The only way to get rid of it is by repenting and washing it away (wash in bucket of water)......relate how you want.

Fourth lesson-

Have dark cola in a clear container or cup. Tell them that this represents us. When we sin- we'd like to hide it and not let anyone know. (Put the buttons in the cola).  These buttons represent sin.  Once they are in- you can't see them.....but over time- the sins rise up and they are seen (the carbonation lifts the buttons to the top) We can't hid sin- so we might as well repent.... relate how you want.

After these lessons- explain how Jesus paid for our sins and how we use the atonement to repent. Now- this is a lot- so you need to move fairly fast.  Throw in some Primary songs and you have a full lesson. Guaranteed to keep the kids attention the whole time!