It's okay to put a 7 year old boy in diapers during the day for wetting his pants, but it shouldn't be a punishment.
However having your 7 year old son wear a diaper when he's wetting his pants can help keep his pants dry and keep furniture and carpets dry as well and protect his health.
Still if you put your 7 year old son in diapers for wetting his pants, he should also see his pediatrician to rule out any medical issue although it's also common for some 7 year olds and younger to wet their pants from simply being too busy with play and ignoring their bladder.
Parents Choice also comes in a size 8 diaper that would fit a 7 year old boy as well and they are also good for bed wetting as well.