Deserialization returns null properties (JsonSerializer)

Question

I know there is a lot of questions about this on SO but I still can't figure why this deserialization is not working. Maybe one more pair of eyes helps me with this.

I have this DTOs:

public class BasicDTO
{
   public OperatorEnum Operator {get;set;}
   public List<BasicChildrenDTO> Children {get;set;}
}

public class BasicChildrenDTO
{
   public string Name {get;set;}
   public ChildOperatorEnum Operator {get;set;}
   public string Value {get;set;}
}

Then I have a windows form text box where I input a json and my methods is like this:

private void button1_Click(object sender, EventArgs e)
{
   var str = textBox1.Text;

   var object = JsonSerializer.Deserialize<BasicDTO>(str);
   //more Code
}

But when I debug my object it came with all properties as null and enums as default. But, deserializer recognize how many objects are in the list, so in my json put 1, 2 or x children object children length is 1, 2 or x (but with null properties).

I Tried the special paste with my json to look for any errors and this is the result

public class Rootobject
{
    public string _operator { get; set; }
    public Children[] children { get; set; }
}

public class Children
{
    public string name { get; set; }
    public string _operator { get; set; }
    public string value { get; set; }
}

Any help? Thank you

EDIT This is my json code:

{
  "operator": "OR",
  "children": [
    {
      "name": "Foo",
      "operator": "EQUALS",
      "value": "Foo"
    },
    {
      "name": "Bar",
      "operator": "EQUALS",
      "value": "Bar"
    }
  ]
}

And this is how is received:

"{\n "operator": "OR",\n "children": [\n {\n "name": "Foo",\n "operator": "EQUALS",\n "value": "Foo"\n },\n {\n "name": "Bar",\n "operator": "EQUALS",\n "value": "Bar"\n }\n ]\n}"

I'm using System.Text.Json and I tried both with lower and capitalize first char but none of them worked.

EDIT 2

This question is already close and answered but I edit with my correct code for anyone helps. My two problems was that my deserializacion becames with null properties because the case-sensitive problem. Then I had problem with the deserialization of the enums. So my final code for that was:

private void button1_Click(object sender, EventArgs e)
{
   var str = textBox1.Text;

   var options = new JsonSerializerOptions
   {
      PropertyNameCaseInsensitive = true,
      Converters = { new JsonStringEnumConverter() }
   };

   var object = JsonSerializer.Deserialize<BasicDTO>(str, options);

//more code
}