In reply to Jintu K Joseph:
Please use code tags. I have added them for you.
You are referencing pktt in your covergroup. You will need to create a handle for pktt prior to creating your covergroup:
baby_pkt pktt;
function new(string name = "baby_coverage", uvm_component parent);
super.new(name, parent);
pktt = new("pktt");
baby_covergroup = new(); //[ERROR]
$display("baby_covergroup object created");
endfunction