No word feels great which is pretty sad considering how many child-friendly euphemisms there are for a penis. With my daughter we try to emulate the same vibe as ‘willy’ combined with some anatomical accuracy by using the word ‘vulvy’. Sounds gross to many, makes sense to others. Your mileage may vary haha.
There are actually things websites can do which may be more common than you’d think. At a high level you could convert all the custom colours to HSV format and slightly lower the value and saturation according to some function. This is fairly common for images.