Tip: Keep those outgrown summer pants and shorts!
During the winter, my son wears a 4T pant. But in the summer, the size of his shorts and pants runs anywhere from 12 months up to 4T. Like a lot of kids, he has grown in height over the years but his waist? Not so much. Toddlers have proportionately large bellies and those bellies don't grow at the rate everything else does.
When long pants grow short, we wear them as capri-length pants, often rolling them up at the bottom. My son prefers them to shorts because his knees don't hurt as much when he falls, and they look GREAT. He gets compliments all the time on several pair of his "baby" pants, which he wears with knockoff Crocs. Of course, cut-offs are always an option as well.
The same applies to shorts he has outgrown; shorts are fit so long these days that the smaller sizes in many cases fit and look even better than the ones designed for kids his size.