The following seems to work for me... the test.bat script simply contains echo "inside batch script":

Update: added wait() call and associated output. Note that without wait(), child procs could become zombies. The call to wait() can be at the very bottom of the script, inside of a parent block.

use warnings;
use strict;

my $pid = fork();

if ($pid){
    print "parent...\n";
}
else {
    sleep 2;
    system "test.bat";
}

if ($pid){
    print "parent: doing stuff...\n";
}
else {
    print "child: exiting\n";
}

if ($pid){
    print "parent: done doing stuff, waiting...\n";
    wait;
    print "parent: children dead, safe to exit\n";
}
[download]

Output:

parent: doing stuff
parent: done doing stuff, waiting...

"inside batch script"
child: exiting
parent: children dead, safe to exit
[download]