don't know if this will help, but i use them, they sell ear plugs that you put in about half hour or so before you land or take off, i am not sure if they have them for kids though. i know rite aid , walgreens, cvs all have them, they helped me i had to fly 2 times within a week with a head cold. one time was a plane change too. and they helped alot.
good luck,
i am taking mine just in case next month.