weeeeeeeeeeell what the hell??!?! It worked for my friend. Maybe when you put the age of the child in the box it has to match the size of the available free diapers they have left (size three). IDK... sorry!
if you use tampons, you can get free samples from playtex and tampax. these both worked for me! i didn't do the diaper registration because i'm still ttc ahaha.
hope this one works!
http://walmart.triaddigital.com/In-Stores-Now-free-samples.aspx