C# Online Compiler | .NET Fiddle

using System;
using System.Threading;
using System.Threading.Tasks;
					
public class Program
{
	public static void Main()
	{
		//DetachedTask();
		//ParentWaitingForDetachedTask();
		//CreatingAttachedChildTask();
		PreventChildFromAttaching();
	}
	
	private static void DetachedTask() 
	{
		var parentTask = Task.Factory.StartNew(() => {
			Console.WriteLine("Parent task executing");
			
			var childTask = Task.Factory.StartNew(() => {
				Console.WriteLine("Child task executing");
				Thread.SpinWait(500000);
				Console.WriteLine("Child task completed");
			});
		});
		parentTask.Wait();
		Console.WriteLine("Parent task completed");
	}
	
	private static void ParentWaitingForDetachedTask() 
	{
		var parentTask = Task.Factory.StartNew(() => {
			Console.WriteLine("Parent task executing");
			
			var childTask = Task.Factory.StartNew(() => {
				Console.WriteLine("Child task executing");
				Thread.SpinWait(500000);
				Console.WriteLine("Child task completed");
				return "success";
			});
			
			Console.WriteLine(childTask.Result);
		});
		parentTask.Wait();
		Console.WriteLine("Parent task completed");
	}
	
	private static void CreatingAttachedChildTask()
	{
		var parentTask = Task.Factory.StartNew(() => {
			Console.WriteLine("Parent task executing");
			for(int i = 0; i < 10; i++)
			{
				Task.Factory.StartNew((taskNo) => {
					Console.WriteLine($"Attached child task {taskNo}  completed");
				}, i, TaskCreationOptions.AttachedToParent);
			}
		});
		parentTask.Wait();
		Console.WriteLine("Parent task completed");
	}
	
	private static void PreventChildFromAttaching()
	{
		var parentTask = Task.Factory.StartNew(() => {
			Console.WriteLine("Parent task executing");
			for(int i = 0; i < 10; i++)
			{
				Task.Factory.StartNew((taskNo) => {
					Console.WriteLine($"Attached child task {taskNo}  completed");
				}, i, TaskCreationOptions.AttachedToParent);
			}
		}, TaskCreationOptions.DenyChildAttach);
		parentTask.Wait();
		Console.WriteLine("Parent task completed");
	}
}

 
using System;
using System.Threading;
using System.Threading.Tasks;
                    
public class Program
{
    public static void Main()
    {
        //DetachedTask();
        //ParentWaitingForDetachedTask();
        //CreatingAttachedChildTask();
        PreventChildFromAttaching();
    }
    
    private static void DetachedTask() 
    {
        var parentTask = Task.Factory.StartNew(() => {
            Console.WriteLine("Parent task executing");
            
            var childTask = Task.Factory.StartNew(() => {
                Console.WriteLine("Child task executing");
                Thread.SpinWait(500000);
                Console.WriteLine("Child task completed");
            });

Cached Result

Process started..

Worker #1234567890 - Total Worker Flight Time: 26
Worker #1234567890 - Worker Work Time Details: [Block Start: 12/30/1899 8:30:00 AM Block End: 12/30/1899 11:45:00 AM In-Out Count: 3] The worker is out of the block for more than 15 min
Worker #1234567890 - Total Worker Flight Time: 23
Worker #1234567890 - Worker Work Time Details: [Block Start: 12/30/1899 1:15:00 PM Block End: 12/30/1899 5:00:00 PM In-Out Count: 3] The worker is out of the block for more than 15 min

Summary
-------
Worker #1234567890 worked in block(s) 1, 2
Worker #1234567890 didn't work in block(s) 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15

Worker #1234567891 - Total Worker Flight Time: 16
Worker #1234567891 - Worker Work Time Details: [Block Start: 12/2/1899 8:30:00 AM Block End: 12/2/1899 11:45:00 AM In-Out Count: 1] The worker is out of the block for more than 15 min
Worker #1234567891 - Total Worker Flight Time: 25
Worker #1234567891 - Worker Work Time Details: [Block Start: 12/3/1899 8:30:00 AM Block End: 12/3/1899 11:45:00 AM In-Out Count: 3] The worker is out of the block for more than 15 min
Worker #1234567891 - Total Worker Flight Time: 180
Worker #1234567891 - Worker Work Time Details: [Block Start: 12/4/1899 1:15:00 PM Block End: 12/4/1899 5:00:00 PM In-Out Count: 1] The worker is out of the block for more than 15 min
Worker #1234567891 - Total Worker Flight Time: 16
Worker #1234567891 - Worker Work Time Details: [Block Start: 12/5/1899 8:30:00 AM Block End: 12/5/1899 11:45:00 AM In-Out Count: 1] The worker is out of the block for more than 15 min
Worker #1234567891 - Total Worker Flight Time: 16
Worker #1234567891 - Worker Work Time Details: [Block Start: 12/6/1899 1:15:00 PM Block End: 12/6/1899 5:00:00 PM In-Out Count: 1] The worker is out of the block for more than 15 min

Summary
-------
Worker #1234567891 worked in block(s) 4, 5, 6, 7, 8, 9, 10, 11, 13, 14
Worker #1234567891 didn't work in block(s) 1, 2, 3, 12, 15

Process finished..