As young children in England in the late sixties and early seventies, my sister and I were introduced to sleeping nude at a very early age. Our parents, possibly somewhat unconventionally for that era, habitually slept in the nude themselves (and still do, even though they are both now in their seventies), believing on health grounds that the less one wore in bed the better, and they were keen that my sister and I should experience the benefits of sleeping without nightclothes as soon as possible. Once we were reliably dry at night, we were put to bed in our birthday suits, and we grew up to accept this as the normal way of sleeping.
Mum always said that it was much healthier to take everything off at night, especially underwear that you've been wearing all day, and that once you've had a shower or bath at bedtime, there isn't much point in putting clothes back on again. I still remember Grannie thinking that it was not only odd, but somewhat improper, for young girls to sleep in the nude, especially when we first went to stay overnight without any nightclothes, but once she got used to the idea, she thought it 'rather cute' that kids should sleep as naked as the day they were born. In the end, she turned nocturnal nudist too!
To the best of my knowledge, we never owned "proper" nighties or PJs. On the rare occasions when it was necessary to dress for bed, generally when sleeping away from home, we reluctantly wore our briefs, but never anything more. Once we reached puberty, even this minimal nightwear attracted parental disapproval, and birthday suits became required year-round night attire, Mum arguing convincingly that, like Marilyn Monroe, all any young lady needs in bed, with the possible exception of a young man, is a dab of perfume and her birthday suit. My husband had a similar upbringing; although his parents never actively discouraged nightwear, they didn't actively encourage it either, and he and his sister were both regularly sleeping naked by the time they entered their teens.
When our own children came along, we made the decision that we ourselves would continue to sleep nude, that we would ensure that our children were aware of this, that we would encourage, but not compel, our children to follow our example on hygiene and comfort grounds, and that we would provide nightwear should the children feel the need for it. In the event, all three of our children, two girls and one boy, now all in their late teens/early twenties, needed little encouragement; after all, what child could resist the opportunity to be legitimately naked for more than a third of the 24 hours! Since they were old enough to choose what to wear to bed, none of our youngsters has ever shown any interest in sleeping in anything other than their birthday suit and the occasional piece of jewellery, and our house, like many others, is effectively a nightwear-free zone.