When I delete a parent issue any children of that issue can also be deleted in Jira?

[Shadish Kumar]

Our project has many tasks and associated sub-tasks. I expect when i delete the parent issue/task, all his associated child issue/tasks be deleted.

[Petter Gonçalves]

Hello Shadish,

By default, all associated sub-tasks are deleted together when you click to delete the parent issue.

There's a warning pop-up informing this when you click to delete the issue:

Let us know if you have any other questions. :)

[Payne]

Note that the general consensus among folks here on the forum is not to delete issues, as doing so can come back to bite you in many ways. Instead, close them with an appropriate resolution (Canceled, Deleted, etc.) As it applies to your particular question, though, you will need to create a post function to close the subtasks. We use the JMWE "Transition Linked Issues" post function for this purpose.