I have 3 tables having a one-to-many relationship with one another:

I am creating the middle InBetween entity with the linked side entities:

Parent parentInstance = new Parent();
InBetween inBetweenInstance = new InBetween(parentInstance);  // Telling it about the parent
Child childInstance = new Child(inBetweenInstance);           // Telling it about the InBetween

So effectively I told each Many-relationship entity about its parent. But the parent One-relationship entity does not know about the children.
I know with hibernate there is this bidirectional relations where the one entity knows about the other vice versa but here I have not set both.

When I am persisting the middle entity I want to insert all 3 at once:

dbService.saveInBetween(inBetweenInstance);

The dbService.saveInBetween is using the InBetween entity class that extends PanacheEntityBase to persist it to the DB.

@Transactional
public void saveInBetween(InBetween inBetween) {
    InBetween.persist(inBetween);
}

What is the problem

Upon retrieval of the InBetween records, by calling the InBetween.listAll() method, I get the Parent entities back but not the Children.
If I look in the database nothing was inserted into the child table.

If I change the code to tell the InBetween instance to also know about the Child, thus so both know about one another it works:

Parent parentInstance = new Parent();
InBetween inBetweenInstance = new InBetween(parentInstance);

// Both the Child and InBetween instances know about each other now
Child childInstance = new Child(inBetweenInstance);               
inBetweenInstance.setChildren(List.of(childInstance));                  //Added this
        
dbService.saveInBetween(inBetweenInstance);

I did not tell the Parent about the InBetween instance but I do need to do the same for with the child.
My question is why is the behaviour different and what is the correct approach in doing it?

I added a minimum code project to Github and my classes are listed below:

3 entity classes:

@Entity
@Getter
@NoArgsConstructor
public class Parent extends PanacheEntityBase {
    @Id
    @GeneratedValue
    private Long id;

    @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL)
    private List<InBetween> inBetweens;
}

@Entity
@Getter
@Setter
@NoArgsConstructor
public class InBetween extends PanacheEntityBase {
    @Id
    @GeneratedValue
    private Long id;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "parent_id")
    private Parent parent;

    @OneToMany(mappedBy = "inBetween", cascade = CascadeType.ALL)
    private List<Child> children;

    public InBetween(Parent parent) {
        this.parent = parent;
    }
}

@Entity
@Getter
@NoArgsConstructor
public class Child extends PanacheEntityBase {
    @Id
    @GeneratedValue
    private Long id;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "inBetween_id")
    private InBetween inBetween;

    public Child(InBetween inBetween) {
        this.inBetween = inBetween;
    }
}

With the DBService class

@ApplicationScoped
public class DBService {

    @Transactional
    public void saveInBetween(InBetween inBetween) {
        InBetween.persist(inBetween);
    }

    public List<InBetween> findAllInBetweens() {
        return InBetween.listAll();
    }
}