Huggies Snug and Dry size 7 diapers should fit a 7 year old boy.
My 7 year old son who is urinary incontinent wears a size 8 Luvs diaper, although he can technically fit into a size 7 Luvs diaper.
He's also fit and still fits into a size 7 Huggies Snug and Dry diaper and wears them sometimes, especially when he needs more absorbency.
Luvs are cheaper than Huggies Snug and Dry, but Huggies Snug and Dry can be worth it for more heavy wetters.
Even a 8 year old to 10 year old might fit into a size 7 Huggies Snug and Dry diaper and other size 7 and size 8 diaper as long as they are not overweight or too heavily built.
If the 7 year old or older child is heavier weight or built larger, then they will often need a Youth sized diaper.