class aggregateRoot {
private List<Child> children = new ArrayList<Child>();

//Noone is allowed to modify the collection without the root knowing.
public List<Child> getChildren() {
  return Collections.unmodifiableList(children);
}

public void removeChild(Child child) {
  children.remove(child);
}

// New Childs can only be added to one aggregateRoot.
// There is no way to add a Child to more than one root.
public Child addNewChild() {
  Child newChild = new Child();
   children.add(newChild);
  return newChild;
}

}

class Child {

// Properties....

// Child cannot live on its own, so only aggregateRoot can create a Child.
protected Child() {};

}