You can include child work items while copying a work item and creating a new instance from it. Copy child work items could be very useful when you want to create a new work item from existing items which has several other work items associated.
Copy Child Work Items in Azure DevOps
To copy a work item, from the work item, select “Create a copy of work item” option
Related Tip: Link Azure DevOps work items to an existing build
While copying a work item, choose “Include child work items” to the copy associated work items.
This option will copy the work item and copy all child work items (up to 100).