The character 肚子 is formed by combining the character 肚, which means "belly" or "abdomen" and is itself composed of the "flesh" radical (月) on the left to signify a body part, with the character 子 on the right. Here, 子 functions not as the word for "child", but as a very common and often meaningless grammatical suffix added to nouns, which in this case transforms the core concept of "abdomen" into a more colloquial, everyday word for "stomach" or "belly".