"气球" is the Chinese word for "balloon." In Engpsh, you can write it as "balloon" and pronounce it as "buh-LOON." Here is an example sentence using "balloon" in a sentence:

"I bought a red balloon at the carnival."

Alternatively, you can also describe a balloon using the phrase "inflatable toy," pke this:

"I blew up the inflatable toy and tied it to the end of a string."