foreach my $c ( @{$child_aref} ) {
                @{$child_aref} = grep { $_ ne $c } @{$child_aref} if ( waitpid($c, WNOHANG) < 0 );

##</code><code>##

If any part of LIST is an array, "foreach" will get very confused if you
add or remove elements within the loop body, for example with "splice". So
don't do that.