An abacus is an excellent resource for helping your child understand 2-digit numbers up to 99. It shows clearly the two columns, the ones and the tens. In other words the 2 yellow balls in the tens column have a value of 20 whilst the two balls in the ones column have a value of 2. This will also help later when multiplying by 10 as they can see each digit moving one place to the left.

Using part whole models with 2-digit numbers.

Fill in the missing numbers in these part-whole models.

Using base 10 blocks with 2-digit numbers.