+1 to calling it what it is. Why do you need a “cute” name for body parts? Also as a PP pointed out, it’s really important that they know the correct names for their genitalia in case (God forbid) they were to be touched inappropriately there. Here’s an article with more information:
https://www.nytimes.com/2016/10/31/well/family/teaching-children-the-real-names-for-body-parts.html
“There are several reasons it’s important for young children to learn the anatomically correct terms for their genitals, Dr. Wurtele said. Knowing the terminology may make children less vulnerable to sexual abuse; prospective offenders may understand that children who are comfortable with the right names for body parts are children whose parents are willing to discuss these subjects, and children who probably will have been told about the kinds of touching that are not O.K.”