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 that have 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
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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.
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This option will copy the work item and copy all child work items (up to 100).
Want to develop custom solution using Azure DevOps – Check this out : Exploring Azure DevOps APIs