Firebase Datasnapshot Json to Object using JsonUtility

I have a json from Firebase DataSnapShot using GetRawJsonValue. I have trouble converting it into object using JsonUtility.FromJson>(myjsonfromGetRawJsonValue). The sample json is as following:-

{"-LRpiJg_RP2re3UY30fG":{"orderslist":[{"Name":"Velvet Cake","Price":"10.9","Qty":1},{"Name":"green tea cake","Price":"8.9","Qty":1},{"Name":"latte","Price":"9.9","Qty":2},{"Name":"americano","Price":"5.9","Qty":2}],"rest_id":"dessert_house","table_number":"123","take_away":false,"user_id":"null"}, "-LRpjHchYhXTa0vY51JX":{"orderslist":[{"Name":"Velvet Cake","Price":10.899999618530273,"Qty":2},{"Name":"green tea cake","Price":8.8999996185302734,"Qty":1},{"Name":"latte","Price":9.8999996185302734,"Qty":2}],"rest_id":"dessert_house","table_number":"123","take_away":false,"user_id":"null"},"-LRplEOFsZ2j3A-aQYT4":{"orderslist":[{"Name":"Velvet Cake","Price":10.9,"Qty":1},{"Name":"latte","Price":9.9,"Qty":2},{"Name":"americano","Price":5.9,"Qty":1}],"rest_id":"dessert_house","table_number":"123","take_away":false,"user_id":"null"}  

The serializable:-

[Serializable]
public class Orderslist
{
    [SerializeField]
    public string Name;
    public double Price;
    public int Qty;
}

[Serializable]
public class Orders
{
    [SerializeField]
    public string user_id;
    public string rest_id;
    public string date_time;
    public bool take_away;
    public string table_number;
    public List<Orderslist> orderslist;

And how to access the children since the object child is System.String using Dictionary?

Unity’s JsonUtility is only meant to map actual classes and in many cases is not suitable for communicating with arbitary web apis.

You can use my SimpleJSON to parse arbitrary JSON data. Note that your sample data is missing a closing curly bracket at the end.