ok, your son may hate the wheelchair just as much! those chairs are hideously uncomfortable for a fully-grown adult, much less a 10 yr old, and have NO support. in fact, i have had my hips (chronic dislocations) get WORSE sitting in them.
you can rent a pediatric wheelchair either at home (as airports are huge!) or in the area. you can just push it empty or filled with coats/souvenirs until he needs it. you can park it with strollers, too... you can also fold it up just like the stroller and carry it on the bus, so you dont have to use the lift...
in fact, his pediatrician may be able to get insurance to pay for a rental, or he may know of a loaners closet at a hospital nearby.
the footrests do NOT fold up and do NOT adjust on the rentals, and it is a mesh seat sling, which stetches around the rivets on the sides and causes "bumps" in the chair under your rear. it was terrible! it was way too big for me, and I am only 5 ft tall/100 lbs. i would look into other options, just in case