It is much easier for your child to understand 100 as a pattern of 10s, rather than one large group of numbers. For example, make a pile of 10 Cheerios, and have your child count them. Then, make ten groups of ten Cheerios, and have your child count by 10s to reach 100.

It's much easier to count to 100 if you can help the child think of it as a pattern of 10s, rather than a huge list of 100 numbers. Once the child can easily count from 1-19, move on to counting in multiples of 10 until you reach 100. These numbers are 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100.