Here are some alternative and more polite ways to say "poop" in Spanish:
* Caca (informal and rude)
* Popó (informal and slightly less rude than "caca")
* Heces (formal and neutral)
* Deposiciones (formal and neutral)
* Materia fecal (very formal and clinical)
It's best to err on the side of caution and use the more polite options unless you're in a very informal setting with close friends.