Sometimes there are lonely children.
If you know a lonely child, there are things you can do to lift that loneliness.
First, talk to the child. What does he or she love or wish for.
Next, find small groups that share that interest--join the child in attending those groups. Engage in the activities and discussions of interest.
Further, scaffold playdates and friend events, but joining your child and choosing an activity that's fun for everyone--an activity that doesn't require lots of talk or your child's investment, but one that's simple and fun.
Tell your child too that it's okay to enjoy being alone and doing quiet things--not every child is gregarious and outgoing, many are quiet and shy. For many children, there favorite times are times at home with the intimacy of the family they love.
I don't like to see a child suffer from loneliness, and at school we seek to support children if they feel this way. This is important.