gistfile1.json

{
  "parents" : [ {
    "id" : 1,
    "name" : "DADDY",
    "children" : [ 1, 2 ]
  } ],
  "children" : [ {
    "id" : 1,
    "name" : "JUNIOR"
  }, {
    "id" : 2,
    "name" : "JUNIOR'S SLUT SISTER"
  } ]
}

Main.java

package org.photon;

import com.fasterxml.jackson.annotation.*;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.io.IOException;
import java.util.*;

public class Main {
    @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
    public static class Parent {
        public long id;
        public String name;

        @JsonIdentityReference(alwaysAsId = true)
        @JsonManagedReference
        public Set<Child> children = new HashSet<>();
    }

    @JsonIdentityInfo(generator = ObjectIdGenerators.PropertyGenerator.class, property = "id")
    public static class Child {
        public long id;
        public String name;

        @JsonIdentityReference(alwaysAsId = true)
        @JsonBackReference
        public Parent parent;
    }

    public static class Registry {
        public Set<Parent> parents = new HashSet<>();
        public Set<Child> children = new HashSet<>();
    }

    public static void main(String[] args) {
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(SerializationFeature.INDENT_OUTPUT, true);

        Parent parent = new Parent();
        parent.id = 1;
        parent.name = "DADDY";

        Child child1 = new Child();
        child1.id = 1;
        child1.name = "JUNIOR";

        Child child2 = new Child();
        child2.id = 2;
        child2.name = "JUNIOR'S SLUT SISTER";

        child1.parent = parent;
        parent.children.add(child1);
        child2.parent = parent;
        parent.children.add(child2);

        Registry registry = new Registry();
        registry.parents.add(parent);
        registry.children.add(child1);
        registry.children.add(child2);

        try {
            mapper.writeValue(System.out, registry);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}