Size is like the difference between a big elephant and a small mouse. When you look at them, you can see that the elephant is much larger. This means the elephant takes up more space and is heavier than the mouse. Size helps us understand how much space something can take up. Think about your toy blocks. Some blocks are big and some are small. The big block will cover more area on the floor than the small one.
Size can also be like wearing clothes. When you put on a shirt that is too big, it feels loose and hangs down. A shirt that is too small might feel tight and uncomfortable. We use size to make sure clothes fit just right.
Imagine you are holding a big balloon and a small marble. The balloon is light but takes up a lot of space, while the marble is small and heavy. This shows that size doesn’t always mean something is heavy or light. Size is about how much space something fills, just like how a big teddy bear fills more of your arms than a tiny teddy bear.