Get-ADUser command add user to root domain security group

Hey, Scripting Guy! With the following command as root domain to the Security Group, located in the Child domain only want to enable users to add. But somehow I could not add to the group, type the correct command. I would appreciate if you could help. 

$OU="OU=Accountant,DC=child,DC=domain,DC=local"
$Group="CN=Group,OU=Groups,DC=rootdomain,DC=local"

Get-ADUser -SearchBase $OU -SearchScope OneLevel -LDAPFilter "(&(!memberOf=$Group)(!userAccountControl:1.2.840.113556.1.4.803:=2))" | ForEach-Object {Add-ADPrincipalGroupMembership –Identity $_ -MemberOf $Group}