How to properly create an entry along with child elements?

Question

MongoDB

There are two circuits (details omitted for simplicity):

parent

const parentSchema = new mongoose.Schema({
    title: {
        type: String,
        required: false
    },
    childs: [{
        type: mongoose.Schema.Types.ObjectId,
        ref: 'Child'
    }]
});

const Parent = mongoose.model('Parent, parentSchema);

Subsidiary

const childSchema = new mongoose.Schema({
  title: {
    type: String,
    required: false
  },
  description: {
    type: String,
    required: false
  }
});

const Child = mongoose.model('Child', childSchema);

I create a parent document:

const newCalendar = new Calendar({
titles: "asd",
childs: [
  {
    title: "child1",
    description: "description1"
  }
]
});
return newCalendar.save();

But I am getting an error:

Parent validation failed: childs: Cast to Array failed for value \"[ {тут переданные поля} ]\" at path \"childs\""

PS I tried to google, I could not find the answer. The only thing that comes to mind is to run the children first and pass them _id when saving, but it seems to me very stupid