Here is how to explain the square root to a child using blocks or other similar objects in 3 steps.
Step 1. Begin by telling the child that all 4 sides of a square are equal. Then, give the child 4 square blocks of the same size and then help the child if needed to complete step 2.
Step 2. The goal is to use the 4 blocks to make a perfect square shape. Emphasize that a square has the same number of blocks on each side.
Step 3. Finally, tell the child that the square root is just the number of blocks you need on one side of a square to make a perfect square.
4 Blocks:
4 blocks can be arranged into a square with 2 blocks on each side.
So, the square root of 4 is 2.
Repeat the activity outlined in step 1 to step 3 using 9 blocks, 16, blocks, 25 blocks, and so forth...
9 Blocks:
9 blocks can be arranged into a square with 3 blocks on each side.
So, the square root of 9 is 3.
Tell the child to notice that 2 × 2 = 4 and 3 × 3 = 9 and say that when you multiply the number of blocks on one side by the number of blocks on another side of the square, it will be equal to the total number of blocks you have.
Now try this to reinforce the concept!
Give the child a number of blocks that will not be enough to complete a perfect square such as 8, 14, or 23. Then, tell the child to complete the square.
With 8 blocks for example, the child should say, " well, I need one more block to make the square"
With 23 blocks for example, the child should say, " well, I need two more block to make the square"
Finally, ask again what the square root is!
To make this activity even more fun, you could use pennies or any other objects kids love to play with.