Allow ComboBox to handle one-to-many associations

Suppose the following domain model where one or multiple children can be associated to only one parent and the association is only stored in the children:

If I want to assign children to the parent, I would have to choose a(n input) reference set selector which would require a selection page. If I don't want to use a selection page but want to assign the children to the parent via a dropdown, my only option at the moment would be the Bootstrap Multiselect third party widget that has not been updated for a long time. The only way to use the combo box here would be if the association is many-to-many and stored in both entities.

It would be great if the combo box functionality would be expanded so that it would also allow for one-to-many associations as well.