Pass a reference to the array instead:

$t->sadk_flap_mx_ifd_laser( ifd => \@child_interfaces, flap => $flaps 
+);
[download]

Then dereference it in the subroutine:

sub sadk_flap_mx_ifd_laser {
    my %args = @_;
    my @child_interfaces = @{ $args{'ifd'} };
    my $flap = $args{'flap'};
    ...
}
[download]

Hope this helps!

Update: removed unrelated link to perldsc, the correct doc is perlreftut as pointed out below by haukex.