The importance of balancing chemical equations and the idea of limiting reagents can be difficult for young chemists to understand. To help them, provide students with a chemical equation that's more familiar and interesting to them:
1 box of cake mix + 3 eggs + 2 cups of water --> 24 cupcakes
Then follow up with questions:
How many eggs do I need if I have 2 boxes of cake mix?
How many cups of water do I need for 2 boxes of cake mix?
How many cupcakes will I get with 2 boxes of cake mix?
How many cupcakes will I get if I have 2 boxes of cake mix, 6 eggs, and 2 cups of water?
Take the questions as far as you wish...
when you make the move to "real" chemical equations and you see some eyes start to glaze over, remind them of the cupcakes!