One of the frustrating things about shopping for toddlers and preschoolers is trying to find the right combination of leg length with the correct sized waistband.
My grandson is almost 4 years old, 40 inches tall, weighs about 41 pounds and has a 19 inch waist. I would describe him as very active and a bit on the long legged side.

Most pants that are long enough for him are too big in the waist, and having the child wear a belt isn't always ideal, first you have the problem of finding a belt in the right size, then comes the struggle to get the belt on. Finally, having a young child wear a belt makes it harder for them to use the bathroom without difficulty, which can impede toilet training or make "accidents" a bit more of a probability.

These pants are reasonally priced, I did some comparision shopping for similar pants from major stores (Sears, JC Penny, etc) and these cost a minimum of $5 less than any comparable pair of adjustable waist jeans that I found in my search.

The adjustment is easy to make, there is a system of elastic straps with button holes that pulls out on each side of the waist. It is easy to fasten the straps to the matching buttons on each side. I doubled the straps back and fastened the ends to the button to keep from having a loose end that could get caught in the zipper.
I haved uploaded a picture showing the doubled back elastic strap fastened to the button.

I recommend this jeans, overall the price and the quality make this a good deal for growing boys.

The denim is a medium weight, the stitching on the pair I received was well done with no flaws. There is a reinforcement stitching on each side, just under the pockets, not sure if that was intended as a design element, but it makes the jeans sturdier