my %children;

for my $n ( 1..4 )
{
    my $child = fork;
    if ( !defined $child) { die "fork failed on $n: $!" }
    elsif ( $child == 0 )
    {    # this is what the child does:
        exec 'some', 'process', $n;
    }
    $children{$child} = $n;
}
while ( keys %children )
{
    my $reaped_pid = wait;
    if ( exists( $children{$reaped_pid} )) {
        checkerror_function( $children{$reaped_pid} );
        delete $children{$reaped_pid};
    }
    else {
        # if you get here, better study "perldoc perlipc"
    }
}