Things that are small are little. Children, lower-case letters, lady bugs, and thumb tacks are all small.
This is a comparative word for things that are tiny. A size small shirt won't fit a big person. If you ask for a small favor, it had better not be a big deal. When someone makes you feel small, that's not a physical thing: it means they made you feel bad, like less of a person. A Yorkie is a small dog, but it's not small compared to a mouse. Everything is small (and large) compared to something else.