There are lots of solutions. You could open a pipe to each child process (instead of forking explicitly) and pass back information from the child to the parent. You could open a filehandle to a temporary file (there's a CPAN module for good temp files) and use that for each child... when you catch SIGCHLD, open the temporary file and append it to the log. You could tie a filehandle to a scalar (Tie::Handle, I believe) and print to that, though you might have to mark it as shareable. (Who knows how far the magic extends across forks?)

If I were you, I'd go the temporary files route. Getting flocks to work well across forks seems tedious to me.

Update: As Abigail points out, flocking after the fork is indeed the way to go. I'm backwards on this one! heh