Before Deleting verify the user can delete and then confirm they want to delete. Then Delete childs

I feel like I should know how to do this but I'm struggling a bit to make it work.

I have added a Delete custom button to the edit page.

When the user clicks on the delete button, I want to check and see if there are children records and if so give them a fairly lengthly message telling them they can't delete the record.

If there are no child records, I want to put up a message confirming they want to do it, and if they say yes, then I want to delete the record. If they say No, then do nothing.

Thanks for helping my foggy mind.