汚れる is "to get dirty." This is when you make something dirty, aka "to make dirty." You know that this is the version where you make things dirty yourself because when you make someone dirty with all that poop you're flinging, they sue (す) you immediately. This happens a lot.
The reading comes from 汚れる, so if you know that you can read this.
We are out of clean bibs. Our baby boy got them all dirty.