I probably wouldn't do it myself. I definately wouldn't stick anything like a cotton wool bud in his hear as it pushes the wax further in. Especially not with having grommets and all. Maybe take him to the GP. They might syringe his ears (if it's safe to do that without the risk of dislodging the gromets). I thought gromets were meant to help drain the ear and clear excess wax? Could it be possible that one or both have fallen out?