Lots of people have reported not receiving the Walmart Exclusive "The Child" Pin With The Vintage Collection 3.75-Inch Din Djarin (The Mandalorian) Set. This was listed and sold as a "Bundle".
The preorder for this bundle that I received yesterday did not include the pin, while my new order placed on 1/12 did include it.
I reached out to our Walmart contacts and basically was told these pins are out of stock currently, so if your order was missing the pin, you are kind of out of luck right now.
They suggested to contact customer service to see if they could offer a discount (not guaranteed) or send product back for refund.