Helping Children Develop Friendships

I've been thinking a lot about children's friendships these days.  One of my kids would rather have his nose in a book or hang out with animals than be with friends his age. 
 
On one hand, I just need to know that's the way God made him.  He might be an introvert.  He is totally happy in his own world.
 
But my mommy heart worries for him.  It's tough to be 'on your own' in middle school.  I long for him to have good friends to support him through the tough transitional years ahead. 
 
If you're in the same boat, you might be encouraged by a few articles I just read: 

6 Ways to Help Your Child Develop Better Friendships

Nobody Likes Me: Helping Children Make Friends | Education.com

I'd love to hear your tips for helping children make friends!