Marketing trick doesn't work here

Tony is diaper trained now. To avoid accident at night, mom bought some Toy story pull-up pants from Costco.
Tony insisted these were diapers. "They are not pants, they are diapers. I am a big boy now, I don't want diapers."
In the end, we have to tell him that he has to wear diaper when he sleeps.
"OK. But they are not pants, they are diapers." Tony said.