Fewer family farms. Mechanized ways of doing things. Coming and going. For some families, summer vacation means a time when children will have a lot of unsupervised time. The modern mindset is that children are provided for when they are having fun with other children their age level.
Children do enjoy other children.
And there is a proper place for group activities. But in the confused values and hectic schedule of this day, children need relationship with their parents more than ever. Many well-meaning parents believe they are providing for their children when in truth they are neglecting them. Children need the security of solid relationship with their parents. No one but parents can provide that for their children.