You can also use mwana (pronounced: m-wanah) which means "child" but can also be used to refer to a son.
It's important to note that Swahili is a gendered language, and the word mtoto (pronounced: m-toh-toh) means "child", but it is generally understood to be a "daughter". You can differentiate between son and daughter by using the word kiume (pronounced: kee-oo-may) for "male" and kike (pronounced: kee-kay) for "female."