Children (and especially infants) have narrower Eustachian tubes (that connect the nose to the middle ear) which are more horizontal than the larger slant that adults have (since we have longer faces). When an eensy weensy air bubble emerges from that tube we hear a "pop". If that tube is clogged and the bubble doesn't emerge, the Eustachian tube still tries to do its job of normalizing pressure so it vacuums its attachment on the eardrum (that stretching is painful!).
To help normalize pressure by opening the Eustachian tube, we can chew gum or yawn which babies (and many young children) can't voluntarily do. This all means that children and babies suffer more pain than adults.
Tips:1. Sucking a bottle/nursing will help. (Since the Eustachian tube connects to the back of the nose, you don't need to worry about air being sucked in from the mouth and going to the stomach.)
2. Decongestants enlarge the Eustachian tube. Some find this helpful to take an hour before LANDING. Absolutely talk to your doctor before giving to infants or children (I wouldn't do it personally.)
3. Painkillers. Again, talk to your doctor.