I would use Huggies Snug and dry diapers for your 7 year old son during the day and at night Huggies overnites which are more absorbent.
Another great absorbent diaper is Gentle steps diapers from Dollar General which are very squishy as well and swell up a lot.
Have him wear just the diaper or just a diaper and shirt like these boys and also give him a bottle and pacifier as well.

