referencial integrity in order for it to work
No. There has to be a defined relationship first, but RI is not required for this particular feature.
Build the parent table. Build the child table. Define the relationship.
NOW build the form for the parent. Build another (smaller) form for the child. Add a sub-form control to the parent with the sub-form wizard enabled.
The wizard will ask you to identify the form that goes into the sub-form. If there is a pre-defined relationship, it will ask you to confirm that the parent & child relationship are the two fields involved in the defined relationship. If so, you are done. (If not, it will ask you to name the parent link and child link field names.)
Thereafter, if you bring up the parent and at least one child exists, you will bring up the child form too. You will have separate navigation tools on the bottom of the sub-form control as well as at the bottom of the parent form.
They are not quite independent. If you change from one child to another, the parent stays put. If you change from one parent to another, the child should change.