Pampers Cruisers Diapers size 7 should easily fit an average sized 7 year old boy.
If the 7 year old boy is of average weight and build then a size 7 Pampers Cruisers or any other size 7 diaper should easily fit him.
If the 7 year old boy is above average weight or overweight then he may need to wear a Youth sized diaper instead.
Another diaper brand that should fit a 7 year old boy are Gentle Steps size 7 diapers from Dollar General.
Or any other size 7 diaper should fit a 7 year old boy just fine.
The Gentle Steps Size 7 diapers are mostly plain white and are less babyish but very absorbent.
They are designed and made for older kids and younger kids that need diapers for incontinence or even bed wetting.