T.cs

using System;
using System.Collections.Generic;
using System.IO;
using Newtonsoft.Json;

namespace Request
{
    public class Settings
    {
        public RequestApi[] RequestApi { set; get; }
    }

    public class RequestApi
    {
        public string ProcessId { set; get; }
        public Children[] Children { set; get; }
    }

    public class Children
    {
        public string FormId { set; get; }
        public Dictionary<string, Value> Value { set; get; }
    }

    public class Value
    {
        public string Id { set; get; }
        public string Name { set; get; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var json = File.ReadAllText("resource/A.json");
            var obj = JsonConvert.DeserializeObject<Settings>(json);

            Console.WriteLine(obj.RequestApi[0].Children[0].Value["agree_to_1"].Id);
        }
    }
}

{
    "requestApi": [
        {
            "processId": "Process_sid-1D5CEC2F-AD25-4724-910B-A4FB70A0EA2D",
            "children": [
                {
                    "formId": "sid-C1A1F9FD-4556-44AE-82C0-5EE45F92A43F",
                    "value": {
                        "agree_to_1": {
                            "id": "yes",
                            "name": "เห็นชอบ"
                        }
                    }
                },
                {
                    "formId": "sid-C458996A-4EEF-4E7C-9C2A-F318FBF0BBB6",
                    "value": {
                        "approve_to_1": {
                            "id": "yes",
                            "name": "อนุมัติ"
                        }
                    }
                },
                {
                    "formId": "sid-CB030662-4451-424D-8A1B-2CA1826AA514",
                    "value": {
                        "agree_to_2": {
                            "id": "yes",
                            "name": "เห็นชอบ"
                        }
                    }
                },
                {
                    "formId": "sid-3690C365-E786-4861-B709-558609E51A92",
                    "value": {
                        "approve_to_2": {
                            "id": "yes",
                            "name": "อนุมัติ"
                        }
                    }
                },
                {
                    "formId": "sid-1D5CEC2F-AD25-4724-910B-A4FB70A0EA2D",
                    "value": {
                        "agree_to_3": {
                            "id": "yes",
                            "name": "เห็นชอบ"
                        }
                    }
                },
                {
                    "formId": "sid-B34D453B-FD7C-4FF9-896E-15F811355216",
                    "value": {
                        "approve_to_3": {
                            "id": "yes",
                            "name": "อนุมัติ"
                        }
                    }
                },
                {
                    "formId": "sid-5EC0CAB8-D128-4733-9476-D3BCF0051FEF",
                    "value": {
                        "approve_to_4": {
                            "id": "yes",
                            "name": "อนุมัติ"
                        }
                    }
                }
            ]
        }
    ]
}