I was a boarding house parent for 4 years before I had my own kids. We took them from 4 years old....
The youngest in my dorms (I covered 4-11yr old girls, 40 kids in total) was a 5 year old. But the boys dorm did have a 4 year old in.
It was in some ways heartbreaking, and I wouldn't send my kids to boarding, but when I saw their lives in the holidays it made me realise that for those whose parents are wealthy but don't want the "hassle" of their kids, boarding was perhaps the better choice. In the holidays the kids would be full time with nannies, would have drivers to take them to play dates/ meet friends/ go to the mall etc. It was sad that they used to say to me "I wish you were my mum" or "please can I stay at school with you?" when their drivers came to collect them for the holidays. Once when a mother came to collect her daughter, the child clung to me, crying, and said "I want to stay with you". I did wonder how that mother felt then.
The thing that reassured me about them being so young and in boarding was that I was there. And that sounds really arrogant, but I knew that I cared. I couldn't be a "proper" parent to 40 girls, but I was around from 6:30am, would do their hair if they asked, would help them make their beds, would tie shoe laces, would chat, would listen to kids read... I tried as much as possible to do "normal" stuff, to make it less regimented (which it obviously had to be to a certain degree to make it work). Then I'd go to breakfast with them, teach all morning, eat lunch with them, spend the rest of the lunch break in the dorm so they could find me for a chat/ would use this time to catch any girl I had a concern about or needed to talk to etc. Teach some of the afternoon (but often had free time thankfully!), then was around in dorm again to mostly just be available. Would stay around for showers (the younger ones would need help, the older ones got their privacy), and to again do hair etc, then ate dinner with them. Whilst the older ones did "homework" I spent time with the younger ones, playing board games or doing "fashion shows" (heaven help me), or doing art and craft etc, then would move around doing this with all the age groups as they finished working. Bedtimes were staggered, so I did a story for each group (even the 11yr olds would beg for a story!), and we would sing a song of their choice before lights out. Inevitably someone would ask for a hug, which let to most of them wanting one, so I would then go round and hug those that wanted and would tuck in any that didn't want a hug. If they wanted a kiss I would let them kiss my cheek and I would kiss the top of their head. Then I would go home (to my adjoining flat), and hope the night was quiet! If anyone was ill, I always asked to be informed (we had 2 other staff who would cover most of the night wakings). Depending on how ill / what was needed, I'd go through, but illness, even mild, was surprisingly infrequent.
There were 2 of us covering the dorm, in addition to the 2 overnight staff. The others cared about the girls and gave them as much attention as I did.
So whilst boarding sounds awful, and I wouldn't at all be able to put my kids into boarding, having been on the other side I can say that, whilst far from perfect and "family"-like, it isn't necessarily entirely isolation and loneliness and nobody there to listen to them or care for them.
I would worry that my kids would not get a caring boarding house parent though, and so would alter my lifestyle in whatever way possible to avoid them boarding. There are parents though who do see it as the best option, for a variety of reasons, and so I just hope most house parents genuinely do care.