After the age of nine years or so, it becomes more likely children will have a 'best friend' and may form more intense, longer-lasting friendships on the basis of a variety of shared interests and things in common.
Your child may be happy with just one friend, or be extremely popular with a large circle of friends. Alternatively, he may seem perfectly content on his own - sometimes because he has interests that are different from most other children his age, whether older or younger. If he's happy with the situation, that's fine. You only need to worry if he seems upset about rejection by friends.
Friendships can be a wonderful source of strength emotionally for children, and help their developing self-confidence.
This can cause enormous anxiety. It's right to worry if your child seems upset by a constant lack of friends. This can mean they're more vulnerable - not just to loneliness and low self-esteem - but to later problems such as lower academic achievement, or even eating disorders and depression.
Your child may be so shy that he has great difficulty reaching out to make friends. Alternatively, a bullying or very aggressive child may find other children avoid him.
However, there are children who don't fit into either of these extreme categories, but who just seem to be loners.
Not all of these children are troubled by it, so it's important not to overreact. While the vast majority of children do rely heavily on their friendships, there are some who seem quite happy without this, and many grow into resourceful, creative adults.