Like this?

use warnings;
use strict;
use threads 'exit' => 'threads_only';

my $ppid = $$;

END {
    return unless $$ == $ppid;
    print "this should print once\n"
}

if (fork)
{
    print "parent\n";
    sleep 1;
}
else
{
    print "child\n";
    threads->exit;
}

print "last line of program\n";

__END__
c:\test>junk2
parent
child
last line of program
this should print once
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