It's a lot cheaper to keep the thermostat at 68 and put clothes on the child, but given that they do heat the house that warmly, perhaps it could be said to be safe enough. Some kids absolutely refuse to keep their shoes on, is it the child's idea or the parents'? Are the child's feet and hands like blocks of ice or do they feel warm (or only slightly cool) to the touch? It seems eccentric to let a child of age 3 run around with not much on during the winter, but unless she is freezing or getting a lot of scrapes and bruises, it is probably not harming her.
I remember the "sleep with your hair wet and get a cold" dictum from old wives during my childhood, but that one has been debunked. (They had volunteers sleep with wet hair, go outside without jackets, etc. etc. and the same number of people got colds with dry hair and warm clothes as with wet hair and no jackets.)
Are you sure they aren't yanking your chain a little bit with this clothing thing? You say "with very little clothing on." Does that mean just a diaper? A shirt and a diaper? And you do mention that the child is the one taking off the clothes. Maybe they are just tired of arguing with her about it, and have decided to reserve their energy for more important issues and turn up the heat, and don't appreciate someone Monday-morning quarterbacking this punt they are doing.
I guess that unless the child was getting sick from this, I would drop the subject unless you think they are actually taking off her clothes and making her walk around for hours like that, which it does not sound like you are saying. She won't do this forever.
All that you said makes sense. My grand daughter just started taking her clothing off during the summer and plays for an hour or so and then puts some of them back on. Now that it is Winter, she has started this again...taking off everything and playing in her play room. My son and his wife just let her and it surprised me when I went to visit and everyone was dressed for winter and my little 3 year old grand daughter buck naked, playing with her toys! And yes, her feet and hands were warm so maybe she is simply warm-blooded. No one made a big deal about it, but it has been 30 years since I have been around babies and thought she needed to have SOMETHING on!!! HAHAHA!!!
Today I caught myself walking around the house with bare feet. I hate to wear shoes...maybe the issue of clothing is not an issue, at least for now!
Also, thanks for the info on the wet hair research! I'm still learning!!!
I'm glad it was useful. Sometimes dealing with a 3-year-old and desired change, it's a lot better to deliberately not make any kind of deal over an action. Maybe your son and his wife have learned that ignoring it is the best way to deal with it, with this child, or maybe they are simply tired of having power struggles with a toddler when there are no costs to letting the situation remain the way it is. She will put on clothes soon enough, and if she's in a confined area and not standing in the front window, all the more reason not to sweat the small stuff.
Recently, I was driving with my 4-year old and I sneezed. I said, "Oh, I sneezed!" and he said "No, mommy, you're supposed to say, 'Damn it! I sneezed." I let it go by at that moment, but casually asked him later who uses that word around him (turns out, a helpful buddy at preschool). Then both my husband and I made a concerted effort to stifle any reaction when our son used it. (It wasn't easy, since such language sounds totally wrong in the mouth of a small child, and also because it was sometimes funny.) But he went past it without getting the idea that he could get a rise out of us with it, and very soon he stopped saying it. If my mother had arrived in the middle of this and said, "Well, honey, I'm sure it is bad for him to use that kind of language, when I was a kid, if we had used such language we would have gotten out mouths washed out with soap," it's possible I would have responded by saying that times have changed, just like your daughter-in-law or son did. (As far as I'm concerned, times have not changed on small kids swearing, but they have certainly changed in terms of how small kids are moved towards dropping unwanted behaviors. They are distracted out of it or not rewarded for it by others' attention, rather than enforced out of it, a whole lot of the time.)
I don't know what kind of conversation went on about your granddaughter's nudity, but if she was warm, she was not in danger. To have someone come in and make remarks might have been already somewhat of a sore point or may have hit on something they are still working on how to handle, maybe they even were having a difference of opinion about how to address it. Mothers-in-law sometimes don't get the full dialogue between their child and his or her spouse about child-raising theory and issues. :)
Take care. I wouldn't worry unless you thought something sexual was going on, and it doesn't sound like the remotest chance that this was happening. Some kids just like to take off their clothes. :)