I agree a little bit with everyone.
Adults need to use their own discretion. Adults have very varying degrees of PH and sweat. Some people sweat easier, more profusely, more smelly. Adults' levels of activity and types of activities vary. I think adults know themselves well enough to know when they need to shower and I have no problem with them showering daily.
Having said that, I don't believe hair needs to be washed daily. At least long hair anyway. I don't think it matters too much with short hair but long hair gets stripped way too often of its natural oils and ends up dry and "needing" hair conditioners and oils and treatments to re-condition it. Same with soap. We use oil-based soaps to try and prevent that whole vicious cycle.
I don't believe most normal kids need to bathe every day. They need hands, face, feet washed but not necessarily a whole bath. They usually get more in the summer than the winter which makes sense but they don't have funky PH yet and their little bodies don't NEED a bath every day just because. And two is truly excessive for a child imo.
Their clothes on the other hand...I'd rather have the extra laundry than put them on again the next day. I realize there were days past when that was necessary and there may be days in the future when it's necessary again, but for the present, it isn't necessary and I do find it unhygenic. Adults can get away with it if they've had a non-active day but kids? I don't know how anyone who has children running around out in the dirt, mud and slime outside, then dropping food and drink and God knows what else on their clothes can put them on again the next day. And babies! With their spit up and blowing through diapers, they require one or two changes in a normal day. And that includes using receiving blankets that catch most of it. I am not afraid of germs but I'm not going to let them fester overnight and have the kids rewear them either. A lot probably depends on the ages of the kids and whether they spend relatively inactive days in school or not but at this point in my family, we change clothes daily.
I think those mulitple daily loads are not just about clothes though. By the time you add up facecloths and towels (daily), kitchen cloths and towels (daily), cleaning rags (daily), sheets and blankets (weekly, unless you have a bedwetter or a baby going through receiving blankets daily) it can rack up very quickly. I also wash our kitchen, entryway and bathroom mats every other week because they get gross pretty fast.
I'm with Elizabeth thanking God daily for running water. I think it's all part of His command to dominate the earth and I believe not using these gifts would be ungrateful. Some may think it's luxurious to change clothes every day. I disagree. I don't believe having more laundry is luxurious lol! But it is part of my duty of state and taking care of my family the best I can.