Kuddos to my mother-in-law, Carol, as well --who is busy sewing--pictures of her alterations to come!
I could find very few images of altered shorts (Mom and Dad haven't tackled pants yet, but don't tempt them), so I am posting what, through trial and error, my parents have created. It seems that there are a few options: Velcro and snaps --and placing either on the side of the shorts or removing the inseam and altering almost like infant pants. Although they purchased a "snap gun" at a fabric store, it did not work, and instead, my dad figured out how to hammer in snaps. I swear he can fix anything --from a lawn mower to a great hem line! He danced for Josh (when he found out the brain tumor was not cancerous) and he sewed for Ethan --that's a Grandpa.
I did find one website that offered altered children's clothing: http://www.adaptiveclothingshowroom.com/. Since my parents won't go into the tailoring business, you might try ordering shorts, underwear, and swim trunks from that site. The products I ordered were of great quality and fit!