I have to admit that I am not a "brand name" sort of person, especially when it comes to my little one who grows so fast. However, I will make an exception for the Carter's cargo shorts with an adjustable waistband. I found these on clearance at a Carter's outlet store, and my only regret is that I didn't buy more!
The inside of the waistband has elastic which is held in place by buttons. You basically pull the elastic (which has buttonholes) as tight as you would like it, and then button it into place. This has been a lifesaver for us - my son is really tall and lanky - and these shorts have been the only cargo shorts that stay up around his waist. If he's not wearing the cargo shorts, he has to wear the cotton gym shorts with elastic waistbands.
These shorts have been put to the test with multiple washings, and look as nice as the day we bought them. This is one instance where the quality of the product is worth the money - I would buy these even if they weren't on sale!