Possibly…
Assuming you are using a native glide form, you could add an On Submit action that adds an extra row to the child table, but it will need to be a custom action, and it would need to check if a child row already exists for that supplier or not. That’s where it gets a little more complicated and fragile. I prefer using a custom form at that point. You would still need a custom action on a submit button with conditions to add rows to both tables or only one table depending on if a supplier row already exists in the child table.