[{"id":"1","todos":[{"id":1,"todo":"todo1","category":"Kitchen"},{"id":2,"todo":"todo2","category":"Kitchen2"}]},{"id":"2","todos":[{"id":1,"todo":"todo3","category":"Kitchen3"},{"id":2,"todo":"todo4","category":"Kitchen4"}]},{"id":"3","todos":[{"id":1,"todo":"todo5","category":"Kitchen5"},{"id":8,"todo":"todo6","category":"Kitchen6"}]}]

db.collection.update({"todos.id":1},{"$set":{"todos.$":{"id":20,"todo":"newTodo","category":"newCategory"}}},{"multi":true})