my %kids;
my $maxkids = 2;

MAIN: while (1) {
    # . . .
    delete $kids{+wait} if $maxkids <= keys %kids;
    if (condition) {
        defined(my $pid = fork) or warn "kaboom!" and last MAIN;
        $pid and $kids{$pid}=1 and next MAIN;
        %kids = ();                 # child        
        my $result = OTHER(@args);  # child
        # . . .                     # more child
        exit 0;                     # child ends
    }
}

delete $kids{+wait} while %kids;

sub OTHER {
    # . . .
}