I think it doesn't have to be awkward. The parents look to you as the 'expert' on kids. So fake it till you make it

Tell them that their daughter may have a yeast infection as her self exploration patterns seem to be escalating. Ask them to take a look and if they see any red bumps or discharge they should bring her to a Dr. If not, then you would like to discuss your standard process for handling in public exploration so that they are consistent at home and d/care.

BTW: My 2yr old has candida (yeast). We would have never gotten in checked if not for the expert observation of her d/care teacher

Now go get em!