Element 'Id' does not match any field or property of class

I got the result from the collection in MongoDB, the structure is the same as below

[DataContract]
public class Father
{
    [BsonId]
    [DataMember]
    public MongoDB.Bson.ObjectId _id { get; set; }

    [DataMember]
    public string Id { get; set; }

    [DataMember]
    public List<Child> childs { get; set; }
}

[DataContract]
public class Child
{
    [DataMember]
    public string Id { get; set; }

    [DataMember]
    public int Name { get; set; }
}

When I try this:

List<Father> f = result.ToList();

It calls Element 'Id' does not match any field or property of the class Model.Child

I think it just takes 'Id' as something else.

How can I deal with it?