For many children, rounding numbers or estimating are very difficult concepts for them to grasp. I think they don't see the point in estimation. What purpose does it serve?
I have a second grader and when he was doing homework on estimation for the first time, he was struggling. He understood the concept well but didn't know why he needs to "estimate". Then when he was given the homework of adding really large numbers (139 + 946) - then he knew why he needs to estimate. Because with estimation, he can just add 100 + 900 = 1000. Adding 100 + 900 is certainly much easier than adding 139 + 946.
I don't know if there is necessary a good way of explaining rounding number and estimation to the your child. Make a number line chart and follow these basic rules work:
1. Rounding to Tens: If the number in the ones value is less than 5, round down. If the number in ones value is less than 5, round up.
For example: 14 rounding to 10
For example: 15 rounding to 20
2. Rounding to Hundreds: If the number in the tens value is less than 5, round down. If the number in tens value is less than 5, round up.
For example: 140 rounding to 100
For example: 150 rounding to 200
Below are some worksheets for your child to practice.
Let' suppose you are rounding 23 to the nearest 10 have the child draw a box around the 2. Next have him/her look at the digit to the right of the number. If it is less than 5 stay with the 2 and write a zero after the 2.(20)
If rounding 57 ,draw a box around the 5 and look at the digit to the right of the 5 . If that digit is 5 or bigger than 5 round up to the ten that comes after 50. That should give 60.