Updated FindAndReturnChildrenByItems to be an extension method

Libraries/SPTarkov.Server.Core/Extensions/ItemExtensions.cs

@@ -191,5 +191,37 @@ namespace SPTarkov.Server.Core.Extensions
 
             return items;
         }
+
+        /// <summary>
+        /// Recursive function that looks at every item from parameter and gets their children's Ids + includes parent item in results
+        /// </summary>
+        /// <param name="items">List of items (item + possible children)</param>
+        /// <param name="baseItemId">Parent item's id</param>
+        /// <returns>list of child item ids</returns>
+        public static List<string> FindAndReturnChildrenByItems(
+            this IEnumerable<Item> items,
+            string baseItemId
+        )
+        {
+            List<string> list = [];
+
+            foreach (var childItem in items)
+            {
+                if (
+                    string.Equals(
+                        childItem.ParentId,
+                        baseItemId,
+                        StringComparison.OrdinalIgnoreCase
+                    )
+                )
+                {
+                    list.AddRange(FindAndReturnChildrenByItems(items, childItem.Id));
+                }
+            }
+
+            list.Add(baseItemId); // Required, push original item id onto array
+
+            return list;
+        }
     }
 }