I'm a 77-year-old grandad who regularly looks after granddaughter and grandson, 11-, 9-year-old respectively. Both grandchildren sometimes wander around naked, although they want privacy when pooing. Me too: although I don't mind if a grandchild wanders in while I'm washing or showering, I draw the line at sitting on the bog. (Wee? - Nobody cares.)
My granddaughter, especially, likes to chat with me when she's in the bath. (A while ago I persuaded their parents that grandson and granddaughter should not share a bath any more, but they're still comfortable around each other naked, albeit they touch less than they used to.)
I persuaded their parents that (as with my own children) the grandchildren should have complete autonomy over their own bodies from the youngest age: "No thank you for tickling!" was something I taught them to say when they didn't wish me or Uncle Jack/Auntie Joan (or anyone!) to touch/tickle them as young toddlers. And I insisted (still do) that Uncle/Auntie (and everyone) respect that wish. That seemed/seems to me much more important than nakedness.
I don't go out of my way to be naked, even in the heat, but it's not a big deal either way. And I do wear underpants when I sleep at grandchildren's house or they at mine - they sometimes climb in bed with me Saturday mornings, and I wouldn't like to be naked then. (At home, just with my wife. I sleep naked, always have: I left my last pair of pajamas behind at my mum's place when I left home in the early 60's.) Weekdays I put on a dressing gown to wake a child for school and leave them to dress themselves.
One day, I expect, perhaps, a grandchild will let me know, tacitly or explicitly, that he/she requires more privacy. That will be fine, also, when/if.
As you might guess, I'm wrinkly and misshapen, something more obvious when I'm unclothed. But, well, this is what it's like being human; I see no need to hide from my children or grandchildren (each of whom is physically perfect, btw). (I have happy memories of helping my own naked, wrinkly, disabled mother to shower and so on, in the years before she died; I'm not ashamed of that, why should I be?)
Oh, and I have other grandchildren I don't get to visit or look after so much. (Different country.) They don't like to see me or others naked, and they keep themselves covered. That's OK too; I'm happy to go along with their/parental habits and customs, and stay clothed more (though I do have to take care remembering where I am sometimes; "If in doubt, clothes on!" is a rule I set myself some years since).
People are different. Children too. There's nothing intrinsically shameful about our bodies, clothed or not; equally, some people like more bodily privacy than others. And children have rights even as against their family members.