PS C:\Users\Administrator> Install-ADDSDomain -Credential (Get-Credential office-2\administrator) -NewDomainName child -ParentDomainName "office-2.local" -InstallDNS -CreateDNSDelegation -DomainMode 7
SafeModeAdministratorPassword: ***********
Confirm SafeModeAdministratorPassword: ***********

The target server will be configured as a domain controller and restarted when this operation is complete.
Do you want to continue with this operation?
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help (default is "Y"): A
WARNING: Windows Server 2016 domain controllers have a default for the security setting named "Allow cryptography algorithms compatible with Windows NT 4.0" that prevents weaker cryptography algorithms when establishing security channel
 sessions.

For more information about this setting, see Knowledge Base article 942564 (http://go.microsoft.com/fwlink/?LinkId=104751).

WARNING: The replication partner: DC-2.office-2.local shows replication errors. You should use repadmin.exe to identify replication errors on the replication partner and resolve them before continuing the installation.

WARNING: Windows Server 2016 domain controllers have a default for the security setting named "Allow cryptography algorithms compatible with Windows NT 4.0" that prevents weaker cryptography algorithms when establishing security channel
 sessions.

For more information about this setting, see Knowledge Base article 942564 (http://go.microsoft.com/fwlink/?LinkId=104751).

WARNING: The replication partner: DC-2.office-2.local shows replication errors. You should use repadmin.exe to identify replication errors on the replication partner and resolve them before continuing the installation.

Install-ADDSDomain : The operation failed because:
Active Directory Domain Services could not create the object CN=CHILD,CN=Partitions,CN=Configuration,DC=Office-1,DC=local. Check the event log for possible system errors.
"An attempt was made to add an object to the directory with a name that is already in use."
At line:1 char:1
+ Install-ADDSDomain -Credential (Get-Credential office-2\administrator ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [Install-ADDSDomain], DCPromoExecutionException
    + FullyQualifiedErrorId : DCPromo.General.54,Microsoft.DirectoryServices.Deployment.PowerShell.Commands.InstallADDSDomainCommand