Preschoolers: Ages 2-5. Preschoolers Need to Say No. For a preschooler sometimes 'no' is not meant to start a power struggle, it's simply an expression of self. 'NO let me do it alone. No, I do it.' It's important to remember that your child may simply be doing his job growing up, and saying 'yes' to himself, rather than 'no' to you..