Here are some examples of irregular noun plurals:
* Singular: Child, tooth, foot, mouse, person
* Plural: Children, teeth, feet, mice, people
These words don't simply add "s" or "es" to form the plural.
It's important to note that the term "irregular" is relative. There are general rules for forming noun plurals, but many exceptions exist.
Do you have a specific question about irregular plurals? I'd be happy to help.