I think the need for friends outside the home gets stronger in the teen years.
At some point, kids WILL wonder what's outside the walls of the house and many WILL want to go exploring. Some might even rebel, depending on their temperament and what the environment is like at home.
Some kids seem to truly NEED friends and socialization, while others seem to get by just fine. It's a question of temperaments.
There are all kinds in the world, don't forget that. To give just one example: some guys would prefer playing football to reading/studying a book on the Python programming language. Others would prefer reading a book about a programming language to playing football with a group.
No, really. I'm serious. I fall into the latter category myself! And there are others like me.
So even if your kids are more shy, etc. don't think that all kids are that way, or that all kids can be that way.
"People" are my favorite subject, and I've done a LOT of reading, observing and thinking about this topic.
I think the key is to make sure children are slowly taught how to deal with the big bad world. Not to throw them in the deep end at age 5 -- that would be disastrous. But as they get older, you trust them more and more, give them more thorough explanations as to WHY we do this and that, etc.
"Because I said so." shouldn't be uttered to a child over the age of 6 -- Unless you want your kids to rebel at the earliest opportunity.
Authoritativeness, passion/zeal, mockery, sarcasm, etc. won't be enough to convince your kids of the virtue of modesty (for example) once they hit a certain age. Eventually they have to adopt your beliefs for themselves. You have to respect them enough to give them a decent explanation.