But...it's their grandparents. It's not like the teenage babysitter you use once every three months is showering with the kids. I dunno....I just don't see what's so icky about my parents being nude with my kids. Jeez....I came out of my mother's body.
For those who send their kids to school (or plan to), are you going to be upset when your kids are made to get naked with all their classmates after gym, with a teacher watching? That started in 7th grade, for me. Far ickier than soaking in the ofuro with my grandma when I was four.
For cultures that like to soak in the ofuro there is no weirdness about nudity between family and it's like a family activity of relaxation and bonding. My Stepmom who is Korean will still scrub down the backs of my half-brothers and both of them are in their twenties and plenty of people get squicked out thinking a mother still does this with her grown sons, but for us it's normal.
As for the kids who go to gym, well the ones that get icked out or are uncomfortable by it? Well I remember plenty of kids who got out of that with a doctor's note.