Shapes and lengths are very important to learn for kids. It forms the basics of geometry for further studies. Comparing lengths are actually a very interesting lesson for kids because they love finding differences between things because it's just fun.
Now for this lesson, you would have to use some interesting and colorful pictures to make comparing for kids interesting.
So simply you will use different pictures of different objects like some flowers, cars, and other such pictures of different lengths. As the kid sees the pictures he/she will start to make the difference of lengths. So here you will make different categories of long, longer and longest.
You will see that kids are actually very intelligent when they have to make a difference in the lengths of things. You can also use objects from your house to make the concept even clear.
Just grab some toys and objects from around the house of different lengths and let the kid sort everything out based on its length. It’s a fun lesson for kids.