A 6 year old child should be potty trained and no longer need to wear diapers at least during the day unless they have incontinence or something else wrong with them that makes potty training impossible.
Some 6 year olds may need to wear diapers during the day or all the time due to special needs or bladder issues.
But if not then the 6 year old child should not be wearing diapers during the day and most 6 year old children would not want to wear diapers because they would say they are too old for them.
Children should be potty trained before 4 years old during the day but if they need to wear diapers at night that is fine too.
My son was potty trained during the day when he was almost 4 years old so he stopped wearing diapers during the day then.
But he continued to wear diapers for bed wetting at night until he quit wetting the bed at age 10.
He was able to wear Pampers size 7 diapers until he was 10 years old so he did wear Pampers diapers at age 6 but only at night and when on a long road trip because he would fall asleep and wet his pants in the car.