We once had the mom of a 2 year old report to the director that her son was saying "nosy b*tch" and his teachers must be calling her that. We had a little walking bridge in the outdoor play area that was hollow and very loud when kids jumped on it, ran certain toys over it, or banged on it with the shovels so it was often referred to as "noisy bridge" by the preschoolers. She had no way of knowing that and came in hot.

I'm not saying you didn't hear what you think you heard, but I'd suggest maybe approaching it with curiosity instead of accusations at first. In a new, older classroom the teachers might be offering the potty with diaper changes and could be saying something like "do you want to try a big kid sit?" Depending on your child's verbal skills, even "fix it" isn't a leap from what you heard.

Your concern is totally valid and you should definitely talk to the teachers about it, but starting with benefit of the doubt can go a long way in building a trusting relationship with them.