If you clone an issue in Jira Cloud with Epic Clone a dialog will be displayed where you can make your configuration for the cloned issue and its child issues. On this page it is explained where to find Epic Clone in a Jira issue. Let's assume we want to clone this issue with Epic Clone:
It contains 3 child issues and 2 linked issues. Child Issue 2 contains 3 sub-tasks. If you now select the three dots → Clone with child issues you will get the clone configuration dialog.
Please proceed on this page where it is explained what you can do when cloning an issue with Epic Clone.