An object lesson will always get a child's (or adult's) attention quicker than a lecture so to teach my children's church class about tithing, I used this object lesson:
Each child had the opportunity to "earn" 10 pennies by learning their memory verse. They had to be able to say it in front of the group.
Once everyone had their pennies, I taught them about giving one tenth to God - out of their 10 pennies they should give 1 to God. I passed the offering plate so those who wanted to put God first could place one of their pennies in the basket. About half of them did and two boys put all 10 of theirs in.
Since I knew some of the children would keep all their pennies, I wanted to show them how God feels about our willingness to give. I brought out bags of bubble gum, telling the children they were 10 cents each. Of course, those who kept all ten of their pennies were able to "buy" a bag with no problem.
"It's not fair!" Those who gave one of their pennies to God sat there frowning and a little peeved with me for collecting an offering before showing them the gum. The ones who kept all ten pennies were gloating while filling their mouths with gum. (Yes - they stuck all five pieces in their mouths at once!)
After the children with 10 cents finished "buying" their gum, I told those with only 9 cents to line up. Then I shared how God will provide for us by allowing our 9 pennies to stretch just as far as our 10 pennies - I offered them the opportunity to buy a bag of gum "on sale" for 9 cents. Then before they sat down, I shared how we can't out give God. Because they gave one penny to Him, He wanted to give them a blessing - a bonus piece of gum which the children with 10 cents did not receive.
Now the ones who kept all ten pennies were starting to feel sorry that they hadn't given one of their pennies to Jesus. One boy even began looking for the offering plate to put one of his pennies in so he could have extra gum. This was a teaching moment because I could tell them that God wants us to give without expecting anything in return.
By this time the two boys who gave all ten cents to God were wiggling up a storm in the back of the room. "What about us? We gave it all to God?"
I invited them up to the front and rewarded them with a bag of gum, plus 10 extra pieces, one for each penny them gave to God.
You really can't out give God. He's proven that in my own life so many times. Perhaps when these boys and girls grow up, they'll remember the lesson of God and the bubble gum and give freely of what they have to Him.