I find it interesting when people fret about 'socialising' their kids, when really all they need to do is interact with them.
I thought the same thing MadB, and I was actually really sad when I realized I couldn't or wasn't giving my DD all she needs. I have house help so no chores to fill my day. So pretty much the whole time was spent interacting with my kids. Lots of outside play, imaginative play, craft, swimming every day, visiting the playground.(with no other kids) I use lots of craft ideas from homeschooling montessori blogs. I had absolutely no concerns about her mental and physical development, but after we returned to Aus it became quite clear really quickly that she was missing those social skills. Maybe she would have got there on her own , I don't know.
I'm still not fretting about the lack of social interaction my kids get though, if I was really concerned we wouldn't be heading back. But kinder has definitely been fantastic for us for a couple of months.

But yes, our situation is kind of the extreme. And generally kids can socialise in other aspects of their life.