using System.Text.RegularExpressions;
public static void Main()
""Characteristics"": ""Nice;Good;""
""Characteristics"": ""Hero;Brave""
string result = Regex.Replace(json, @"(\""Children\""\:(.|\n)*?)(\{(.|\n)*\{(.|\n)*?\}(.|\n)*?\})", (m) =>
return (m.Groups[1] + "\"" + Regex.Replace(m.Groups[3].Value.Replace("\n", " "), @"\s+", " ") + "\"");
Console.WriteLine(result);