Dont use perl, use the Windows Shell.

for(0..4){
print "starting $_\n";
system("start", "perl.exe",  '-e',  'print qq!hello world\n!;sleep 1;'
+);
print "end of starting $_\n";
}
[download]

You will notice the 1st console box will say "end of starting 4" before all 5 new consoles disappear. No pipes, no FDs and no pids to worry about. But you won't know when the childs are done.