ds is 4 and is currently an only, but that didn't factor into my choice to home ed at all!
He gets to play with the kids on the street, at church, at home ed group, and wherever there might be other children, soft play, park etc.
My opinion on the whole socialisation thing is where else in life, apart from school, will someone be expected to hang around with people who were born within the same school year?!
I think it's counter-intuitive for a peer group, especially in the early years, to basically bring themselves up with minimal adult input to help them negotiate the world of relationships and their own emotions.
Home ed group for us is like extended family, a huge ranges of ages, people you like and dislike but have to get along with, other adults who look out for your child and care about them even if on a basic level and who are not just authority figures for your child.
Socialisation also includes how to act and react in the outside world and ds spends a lot more time in that world!
At home ed group, at the end of one session each week the talking stick comes out and the children discuss issues that have come up, in general, or with each other, and they are all able to participate in resolving these.
That's the kind of socialisation I think is important, not whether ds is forced to spend 6 hours a day with children born within the same 12 month period, shut away in a building not out in wider society, and being under the authoritarian control of a handful of adults.
Obviously, this is a response for the OP, I am hardly posting this in education in general. Plus, explaining my beliefs and choices is merely that and does not constitute a specific attack on those who believe differently!