inheritance & random function c# [duplicate]

i have 2 child class and 1 mother class. i defined a rand object in mother and i called it in childs but its doesn't work properly. both int are the same. i want to assign different value

 class Mother
    {
        public int sayi;
        public Random rand = new Random();

        static void Main(string[] args)
        {
            ChildFirst firsCh = new ChildFirst();
            ChildSecond secondCh = new ChildSecond();

            Console.ReadKey();
        }
    }
    class ChildFirst : Mother
    { public ChildFirst() { sayi = rand.Next(1, 100); Console.WriteLine("Random int is: " + sayi); } }
    class ChildSecond : Mother
    { public ChildSecond() { sayi = rand.Next(1, 100); Console.WriteLine("Random int is: " + sayi); } }