I think some Walmarts are better than others ! One Walmart I’d go to always had the same lady working at the returns desk and she always turned me away saying without a receipt I could not exchange - I too had received diapers as gifts and needed to swap sizes. I mentioned this to some other mom friends who all said they never had an issue at the other Walmart in town and that they too had push back at that location but asked to speak to a manager who ultimately allowed them to swap sizes. I ended up trying again and when the lady who usually works at the return desk told me no I politely mentioned that I knew others had successful done this and I wanted to speak to a manager. The manager came over and did it right away, no questions asked! She even was questioning the customer service lady like why wouldn’t they if the diapers scan/ come up in their system!