c#/json.net deserialize child with data from parent

Question

    class Item
    {
    public string Id;
    public List<Item> Children;
    }

json

    {
        "Id" : "/parent",
        "Children" : [
        {
            "Id" : "/child1"
        }
        ]
    }

I have class for creating nested items. How would I have a child item access the parent's Id field during/after deserialization of the child? Or is there a way to send the parent Id field when the child is to be created?

Example: Parent Id "/parent" Child Id "/child1" I want the child Id "/parent/child1"

For reasons, I cannot use '[OnDeserialized]' after the parent is finished to loop children and change Id. Nor do I have access to change the json files themselves.