Sympathize - my ears are, um, challenging and I've ruptured ear drums repeatedly including once on a flight.
What works for me is to take oral decongestant and nasal decongestant (spray or inhaler) just before take-off and again when I feel the plane descending if I can have another dose then. If the flight will be too short to have a second dose of the nasal decongestant for landing, then I take the oral decongestant at take-off and nasal decongestant for descent. I did this with Dr approval - you would need to check dosing and timing for your son with his Dr. These meds can have rebound congestion and can have revved up or other side effects - definitely check with Dr and maybe even give meds once prior to trip to ensure you don't have any unfortunate reactions.
I also clear my ears by holding my nose and mouth closed and either "blowing" out or "breathing" in "through" the nose - no air actually passes in or out of my nose or mouth but it helps equalize the pressure in my ears. This works best if done as soon as ears notice anything - if left too long, the "pop" when ears do equalize is painful. My Dr is OK with this but my mother hates this idea, thinking I am blowing bacteria up into my ears and causing infections - again, I'd check with Dr.
Yawning works much much better for me than swallowing or gum. Sometimes just wiggling my jaw around helps. I think we each have different eustatian tube and ear geometries?
Earplanes have not been helpful to me and I can't stand the feel of them in my ears for more than a few minutes - adult or child size. Maybe if I didn't have my other tricks, the earplanes would make a difference - the science behind them seems good...
Warm heat helps to soothe my ears if they start bothering me. Drinking tea helps as does the thing a flight attendant did to/for me when I (as a 16-year-old) was in tears. The flight attendant thing has helped soothe ear congestion on land when I've tried it during the decades since. You would need hot water soaked paper towels and two insulating cups from the flight attendant. Since I got hot water on my DD once at home, there is a chance that the flight staff won't be allowed to do this for you. Maybe you can get or carry with you two empty cups and a few paper towels (wash-cloths/face flannels would be better) for each cup. The hot water (from the lavatory if you can't get it from the galley) is dripped onto the towels in the bottom of each cup - enough to provide moist heat but not enough to drip out of the towels burning your son. Place these cups of moist heat over the ears and hold them there so that the moist heat can soothe the ears through the ear canal. It looks funny and is a bit of work to put together, but really feels better. I like better
As a grown woman, I always end up in tears, and if we have a connecting flight, I never want to get on it. It takes days for my ears to eventually clear, and in that time I experience ongoing pain and muffled hearing. I have asked many doctors about it in the past, and they have all given me the usual response, try lollies, chewing gum, earplanes, decongestants etc. The only thing that has offered any relief for me is grommets. Since I had them put in, I don't get any pain at all and flying has been a breeze. It's a bit of a drastic measure though for one trip - I do a lot of flying so it's been worth it for me.
This is the best!! When my son was a toddler he had lots of ear pain when the plane was descending. The attendant was right there with the two styrofoam cups with hot paper towels in them. It worked 'instantly' - no more pain! The hot paper towels equalized the pressure on his ears.
