I don't think your processing of $opt_numChilds is doing what you think. Instead of

my $numChilds=3;
...
($opt_numChilds) ? $numChilds=$opt_numChilds : $numChilds;
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try

my $numChilds = $opt_numChilds ? $opt_numChilds : 3;
[download]

Your code gives a "Useless use of private variable in void context" message.

Cheers,

JohnGG