Playgrounds highlight two parental extremes. At one end are parents who, so long as they’re undisturbed while engrossed in their smartphone, couldn’t care less if their offspring swipes other kids’ buckets and sand shovels or shoves them around on a climbing frame. At the other are those who watch over their brood like a hawk, accompany their every move and always have a steadying hand on them when they’re climbing. Most parents fall somewhere between these two extremes, of course, but experts say the number of overprotective parents seems to have grown in recent years, and that this may be ad…