public Statistic Statistic() { var statistics = new List <Statistic>(); statistics.AddRange(stand.Statistic().children); statistics.AddRange(managedParkingBoys.Select(b => b.Statistic())); return(new Statistic { What = "M", num = statistics.Sum(s => s.num), sum = statistics.Sum(s => s.sum), children = statistics }); }