sub interact() {
    print 'Current number of children is: ', "$children", '. i.e. these:', "\n\n"; 
    system('ps -ef | grep tryMore | grep -v grep');
    print "\n\n";
    print 'Minus one for the parent, of course', "\n\n"; 
    print 'How many children do you want to add? [1]: ';
    my $new_kids = <>;
#   ^^ (Your mistake?)
    chomp $new_kids;
    $new_kids = '0' unless $new_kids;
    unless($new_kids) { $children += 1; } else { $children += $new_kids; }
    return; 
}