I give my son Benydryl a 1/2 hour prior to boarding the plane. This opens the ears, nose and throat to lessen clogging. Also, try any type of strong mint (if the kids don't mind it). DH and I use Listerine strips and we have no problems. My son does not like the taste.
Another good remedy is to keep their mouth moving.......... gum, sucking on a bottle of juice, water! The Starburst suggestion is a great one as well. Or toostie rolls.
Good luck!
L