T.C.
Along with all the great ideas everone else has given: can I make a suggestion?
If it's just a muscle-weakness issue, here's a great exercise a dentist gave me once (this exercise is NOT for babies, (who drool anyway,) or toddlers who can't follow directions well - safety first!):
Find a long, thin rubber band and a button about 3/4" to 1" in diameter. (A fatter button with wide holes in it is best). Thread the rubber band through the holes.
Have your child slip the button between his front teeth and closed lips (again: think safety! watch your son while he does this, and don't leave him alone with it!!!). Have him pull gently on the rubber band, and hold the button in place with his lips. Count one... two... three out loud for him, and then have him relax the rubber band.
Do this for 20 "reps", twice a day. If the button pops out of his mouth easily, shorten the count, or start with fewer reps.
As his muscles get stronger (this will "work" the lip, cheek, and tongue muscles), you can use a shorter, thicker rubber band; or a slightly smaller or thinner button; or increase the count time. Make a game out of it so it doesn't get boring; or sing a song (like Row, row, row your boat); or give star stickers... whatever he likes, for doing it.
Once the drooling stops, you can probably quit forever. OR, if the drooling comes back (or never goes away), I'd talk to a Speech Therapist or a Pediatric Ear-Nose-Throat Doc. (ENT)
Good luck!
T
Oh! I just remembered exercise #2!! (sorry). Buy the wide Boba drinking straws (they have them @ Ta-Lin Asian Market in Abq.; or you can nab one or two from a Boba juice bar, and reuse them). Make your son a nice, thick drink, like fruit slush; purple cow; whatever his favorite thick drinks are), and have him try to suck it up through the Boba straw. Combine this with the button ex., and he'll get those muscles firmed up even faster!
T