Thanks for the inputs
Here is the modified code with wait using IPC::ShareLite- still missing data

use strict;
use Parallel::ForkManager;
use IPC::ShareLite;
use Storable qw( freeze thaw );

my $fork_manager =  new Parallel::ForkManager(5);

my $share = new IPC::ShareLite( -key     => 1971,
                                -create  => 'yes',
                                -destroy => 'yes' ) or die $!;

my $hash = {'PARENT' => $$};
$share->store( freeze( $hash ) );

foreach my $child ( 1 .. 10 ) {
    my $pid = $fork_manager->start($child) and next;
    $share->destroy( 0 );
    
    my $hash = thaw( $share->fetch );
   
    while (1) {
        if ($share->lock()) {
            last;
        }
        else {
            print "$$ cant lock share\n";
            sleep 1;
        }
    };
    for my $id (1 .. 20) {
        my $key = $child . '-' . $id;
        $$hash{$key} = qq{|Kid $child pushed $id};
    }
    
    $share->store( freeze( $hash ) );
    $share->unlock;
    
    $fork_manager->finish($child);
}
print "Waiting for Children...\n";
$fork_manager->wait_all_children;

my %final_parent_hash;
my $sleep_ctr = 10;
while ($sleep_ctr) {
    %final_parent_hash = %{ thaw( $share->fetch ) };
    print scalar (keys %final_parent_hash) . "\n";
    if ((keys %final_parent_hash) == 201) {
        last;
    }
    sleep 1;
    $sleep_ctr--;
}

foreach my $child ( 1 .. 10 ) {
    for my $id (1 .. 20) {
        my $key = $child . '-' . $id;
        if (! exists $final_parent_hash{$key} ) {
            print "Missing data for Kid $child , data $id\n";
        }
        else {
            print "$key = $final_parent_hash{$key}\n";
        }
    }
}
[download]

Here is the modified code with wait using IPC::Shareable - works like a charm :)

use strict;
use Parallel::ForkManager;
use IPC::Shareable;

my $glue = $$;
my %options = (
     create    => 1,
     exclusive => 0,
     mode      => 0644,
     destroy   => 1,
);
my %final_parent_hash;

my $parent_share = tie %final_parent_hash, 'IPC::Shareable', $glue, { 
+%options } or die "parent : tie failed\n";

my $fork_manager =  new Parallel::ForkManager(5);

foreach my $child ( 1 .. 10 ) {
    my $pid = $fork_manager->start($child) and next;
    my %options = (
     create    => 0,
     exclusive => 0,
     mode      => 0644,
     destroy   => 0,
    );
    my %child_hash;
    my $child_share = tie %child_hash, 'IPC::Shareable', $glue, { %opt
+ions } or die "client: tie failed\n";
    for my $id (1 .. 20) {
        my $key = $child . '-' . $id;
        $child_share->shlock;
        $final_parent_hash{$key} = qq{|Kid $child pushed $id};
        $child_share->shunlock;
    }
    $fork_manager->finish($child);
}
print "Waiting for Children...\n";
$fork_manager->wait_all_children;
my $sleep_ctr = 10;
while ($sleep_ctr) {
    if ((keys %final_parent_hash) == 200) {
        last;
    }
    sleep 1;
    $sleep_ctr--;
}
foreach my $child ( 1 .. 10 ) {
    for my $id (1 .. 20) {
        my $key = $child . '-' . $id;
        if (! exists $final_parent_hash{$key} ) {
            print "Missing data for Kid $child , data $id\n";
        }
        else {
            print "$key = $final_parent_hash{$key}\n";
        }
    }
}
IPC::Shareable->clean_up_all;
[download]

I think IPC::ShareLite is the culprit
Thanks Aveek