@Getter
@Setter
public class Base {
	private String baseField;
	private Base child;
}

@Getter
@Setter
public class Child1 extends Base {
	private List<Integer> child1Field;
}

@Getter
@Setter
public class Child2 extends Base {
	private List<Integer> child2Field;
}

public class Test {
	public static void main(String[] args) throws JsonProcessingException {
		Base base = new Base();
		base.setBaseField("base");

		Base child1 = new Child1();
		child1.setBaseField("child1");
		List<Integer> child1Field = Lists.asList(1, new Integer[]{1});
		((Child1)child1).setChild1Field(child1Field);

		Base child2 = new Child2();
		child2.setBaseField("child2");
		List<Integer> child2Field = Lists.asList(2, new Integer[]{2});
		((Child2)child2).setChild2Field(child2Field);

		child1.setChild(child2);
		base.setChild(child1);

		System.out.println(new Gson().toJson(base));
	}
}

{
    "baseField": "base", 
    "child": {
        "baseField": "child1", 
        "child": {
            "baseField": "child2", 
            "child2Field": [
                2, 
                2
            ]
        }, 
        "child1Field": [
            1, 
            1
        ]
    }
}

{
    "baseField": "base", 
    "child": {
        "baseField": "child1", 
        "child": {
            "baseField": "child2"
        }
    }
}