Can you create a related section for the child custom object under a parent custom object?

Summary:

We are trying to create a experience that minimize the click of creating child object records after the parent object record is created.

Parent Object: intake form

Child Object: intake form detail.

What we would like to replicate is the experience where after you created an opportunity record, you can directly add opportunity revenue line items as a separate section at the bottom of the opportunity page.

I noticed that's not an option if you have a custom object and a child object underneath it. Did I miss anything? Or is child object can only be created as a subtab for custom objects?