Modelling friendships to a child when you're an adult is just a ludicrous idea
I disagree. My parents have always had friends, and therefore I have always seen this as normal and achievable. Their friends had children, and I spent a lot of time with them. Some became friends of mine, some didn't...it all developed my social skills for later.
My parents have continued to make friends throughout their lives through work, fishing, golf, parish groups, bridge etc. I have always seen them be friendly, reach out to people, expect and receive a good response from others. I have always seen them welcome people into their lives, and the payback in terms of fun and support
If they had been insular and friendless (through choice or otherwise) I would have had fewer opportunities as a child, and I don't think I would have the same social skills and expectations that I have now (such as they are!).
I see a lot of people on Mumsnet who just don't know how to make friends, or don't understand that you can make the first move, or fear rejection, or take offense about tiny things, or can't share friends, or think they can only be friends with people who are just like them. If they had watched their parents maintain healthy friendships, they might be less likely to struggle with these issues.