You'd need to pass the same seed to srand in both processes. You could generate the seed in the parent and pass it to the Perl scripts via the environment or an argument.

$ set seed=$RANDOM  # Or whatever
$ perl -e'$,=" "; $\="\n"; srand($ARGV[0]); print rand, rand, rand;' $
+seed
0.17082803610629 0.749901980484964 0.0963716556235674
$ perl -e'$,=" "; $\="\n"; srand($ARGV[0]); print rand, rand, rand;' $
+seed
0.17082803610629 0.749901980484964 0.0963716556235674
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