I'm going to tell a mom and grandma to try to keep their toddler quiet in the library
Do you think it's really necessary?
It's important to be quiet in the library.
Loud kids can be annoying. But these days, libraries aren't usually super quiet, and it's reasonable for little kids to make some noise there.
I need to work and I can't do it with the noise.
If the noise is so distracting can you ask to borrow a private room from the librarian? If they don't have any they might be asked to leave. It is a public space meant for learning and study.