... it all really depends on your own feelings on it and your kids cues.
I have 2 kids, 4 and 7 years old.
They see us naked.... we don't flagrantly parade around naked on purpose of course, but we just go about normal everyday things like changing clothes or taking a shower. IF they see us naked doing normal things, its fine. We don't act like we got 'caught' doing something 'bad' if they see us. Nor do we scurry around trying to 'hide' our naked body all of a sudden. To me, that is bringing more attention to it.
Our kids know their body parts. They know the difference between boys and girls. They know grown ups have hair in certain places. We don't treat it like a big deal.
My kids also know, about "privates" and 'strangers' and what is inappropriate or not with their bodies. They also know, not to parade around naked themselves, when outside family members are around or when at the beach for example. They know what 'privacy' is... and in conjunction with their bodies. They know, how to say they want privacy if changing clothes etc. They know.
Each family/parent/culture varies. And the child's 'cues.'
In certain cultures, they even take communal baths together... or sit in the hot springs together.
ALSO, societal 'rules' on it may vary. If for example an older child tells their Teacher that they saw their parent naked or took a bath with them... it CAN be misconstrued.... and questioned. For example: a friend's 5 year old child told her Teacher she sleeps with her parents. No other detail. BUT the Teacher thought it was inappropriate and called CPS on them.
So...
Your kids, are definitely old enough, for you to Teach them about their body parts AND about Privacy AND about their body and strangers...
all the best,
Susan