Updating child array as per parent

main.dart

var json = {
  "Accessories": [
    {
      "id": 1,
      "brand": "samsung",
      "parentId": null,
      "children": [
        {"id": 4, "name": "Ace", "parentId": 1},
        {"id": 5, "name": "note", "parentId": 1},
        {"id": 6, "name": "galaxy", "parentId": 1}
      ]
    },
    {
      "id": 2,
      "name": "Asus",
      "parentId": null,
      "children": [
        {"id": 7, "name": "gaming", "parentId": 2},
        {"id": 8, "name": "office", "parentId": 2}
      ]
    },
  ]
};

void main() {
  var list = Accessories.fromMap(json);
  list.accessories?.forEach((e) {
    var brand = e.brand;
    if (brand != null) {
      e.children?.forEach((element) {
        element.brand = brand;
      });
    }
  });

  print(list.toMap().toString());
}

class Accessories {
  Accessories({
    this.accessories,
  });

  List<Accessory>? accessories;

  factory Accessories.fromMap(Map<String, dynamic> json) => Accessories(
        accessories: json["Accessories"] == null
            ? null
            : List<Accessory>.from(
                json["Accessories"].map((x) => Accessory.fromMap(x))),
      );

  Map<String, dynamic> toMap() => {
        "Accessories": accessories == null
            ? null
            : List<dynamic>.from(accessories!.map((x) => x.toMap())),
      };
}

class Accessory {
  Accessory({
    this.id,
    this.brand,
    this.parentId,
    this.children,
    this.name,
  });

  int? id;
  String? brand;
  String? parentId;
  List<Child>? children;
  String? name;

  factory Accessory.fromMap(Map<String, dynamic> json) => Accessory(
        id: json["id"],
        brand: json["brand"],
        parentId: json["parentId"],
        children: json["children"] == null
            ? null
            : List<Child>.from(json["children"].map((x) => Child.fromMap(x))),
        name: json["name"],
      );

  Map<String, dynamic> toMap() => {
        "id": id,
        "brand": brand,
        "parentId": parentId,
        "children": children == null
            ? null
            : List<dynamic>.from(children!.map((x) => x.toMap())),
        "name": name,
      };
}

class Child {
  Child({
    this.id,
    this.name,
    this.brand,
    this.parentId,
  });

  int? id;
  String? name;
  String? brand;
  int? parentId;

  factory Child.fromMap(Map<String, dynamic> json) => Child(
        id: json["id"],
        name: json["name"],
        brand: json["brand"],
        parentId: json["parentId"],
      );

  Map<String, dynamic> toMap() => {
        "id": id,
        "name": name,
        "brand": brand,
        "parentId": parentId,
      };
}