using System;
using System.Text.RegularExpressions;
public class Test
{
public static void Main()
{
String input = @"[[Parent1 [[Child 1]],[[Child 2]],[[Child 3]]]] [[Parent2 [[Child 1]],[[Child 2]]]]";
Regex rgx = new Regex(@"(?<parent>Parent\d )|(?!^)\G(?:\[\[(?<child>.*?)]]),?");
foreach (Match m in rgx.Matches(input))
{
Console.WriteLine(m.Groups["parent"].Value);
Console.WriteLine(m.Groups["child"].Value);
}
}
}
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