Here is an object lesson you can do with kids in a Sunday School Class or at home with your own siblings!
Bible Text: Genesis 4:1-16
Memory Verse: Hebrews 9:22b
Craft: Making a fluffy sheep
Explain and memorize the verse
Then tell the story of Cain and Abel. Making sure to explain the reason Cain's offering was not accepted and Abel's was, and why they were offering sacrifices in the first place. (The memory verse should help.) This is a very easy story to put in the plan of salvation.
After that you can have the children sit down and make a fluffy sheep with the memory verse on it to help them remember the meaning of the story...
This is a very simple craft but does take a little prep on your part.
Take a sheet of paper for each child. Draw a large, yet simple sheep in the middle, and outline it with a marker. Then write the memory verse at the bottom.
In class have the children glue cotton balls on the sheep. They can glue the balls on fluffy or they can pull the balls apart a little which ever they want. (Or however many cotton balls you have. ;)
And this is just a suggested way to do it. You can do things in whatever order fits your classroom schedule! Hope this helps someone who's in a pinch and needs a lesson quick! ;)