I have a Many-to-Many relationship set up using the Composite element model which seems to be working.

Parent
Child
ParentChildAssociation

I can insert a Parent without creating a ParentChildRelationship (and I am fine with that). But I can also insert a Child without creating a ParentChildRelationship. That seems like an odd thing.

Question. Is it possible to force the ParentChildRelationship to be created when the Child is inserted?

You have defined a many to many relationship, not a parent-child relationship. Many to many does not have parent-child sematics. If you want to enforce parent child through the data model, you will need to redesign the data model. Hibernate is not involved.

Well maybe a bad example. In my example, a parent can have many children (2 kids in the family) . And a child can have many parents (mother and father).

I am asserting that a child cannot exist without first having a mother and father.

That's OK, but that is not what the data model will enforce as it stands.

You could perhaps use Hibernate to enforce it (because the database won't without changing the model) by intercepting Save for the Child table and validating that they have a parent. See 9.9. Interceptors in the documentation.

If you want to enforce this rule, you can use 2 separate one-to-many relationships.

This will also eliminate the need to have a separate many-to-many mapping table, as your child objects can contain 2 parent references (father/mother). See below:

father(1) -> children(many)
mother(1) -> children(many)

child.getMother()
child.getFather()