Prior to the age of ten, friendship groups are generally unorganized and children show minimal preference for specific playmates. Around the age of ten, children begin to form groups. Older grade school children develop best-friend relationships. Yes, younger children talk about their best friends, or one child with whom they prefer playing, but these younger children also change best friends regularly. And, if their best friend is not available, they will easily play with another child.
The older child, though, can show real allegiance to his best friend. He will frequently talk with this friend on the telephone, will want to be involved with him most of the time in group and play activities, and won't be involved in activities when the best friend is excluded. If this best-friend relationship is so intense your grade schooler can't find anything to do when the best friend is not around, this is a problem. Equally problematic is the older child who has no best friend nor any close friends. As an adolescent or adult, he may well be socially isolated, a loner, uninterested in group activities. As a parent, accept your child's best friends and reference groups, and take time to know these children, for these relationships set the tone for later relationships.
One of your primary responsibilities to your children is to help them select friends and reference groups who share values, beliefs, behavior standards and interests. For your grade school children, your involvement with and knowledge of their friends and associates can help you have some influence on whom they pick as friends and which groups they participate in. To ignore or underestimate this important parental task is to neglect this critically important transition period. But beware: to be too controlling, too judgmental of friends and groups is clearly bigoted and inappropriate. As with all parenting tasks, the right course lies somewhere between totally ignoring your children's friendships and reference groups and giving them no personal freedom or responsibility to select their own friends and groups. your awareness of this parenting task and that the task starts when your children are young will aid you in dealing with your children and their friends in reasonable and productive ways.