Some Jewish people believe that speaking of wealth, good luck or children can bring bad luck or incur the evil eye.
Ways to ward off the evil eye include hamsa which look like an outstretched hand, a red string and the phrase "pooh pooh."
My historical summary specifically mentions the evil eye as that is the superstition that Golde refers to during the show.
Golde says the phrase to ward off the evil eye immediately after mentioning it as well.
Berman, E.(3 Aug 2022.) Magical Thinking: Superstitions and Other Persistent Notions. Retrieved from: https://reformjudaism.org/blog/magical-thinking-superstitions-and-other-persistent-notions