If you have a child with long legs and a small waist, you probably have bought a pair of pants that are just the right length but are too wide in the waist. This can happen even when the pants have adjustable waists. Here is an easy way to fix this problem by taking in the already adjustable waist!
To have an idea of how much smaller you need to make the pants’ waist, measure the size of your child’s waist (50 cm or 20″, for example). Then, pull the adjustable bands in both sides of the pants to their maximum (so that the pants’ waist is at its smallest). Then measure the waist size of the pants (60 cm or 24″, for instance). The difference between the two measurements is how much you want to take in (60-50=10 cm or 24″ – 20″ = 4″, in this case). I will refer to this distance as D (it doesn’t matter whether your D is in cm or inches).
With a tracing pencil or tailor’s chalk, mark a vertical line that is D cm/inches away from one of the existing elastic band openings (in the direction of the fly of the pants). Make this vertical line the same size as the existing opening. (I know that this means you are taking in double the length of D, but, because pant fabric tends to be thick, it does not bunch up easily . So, this seemingly illogical calculation has always worked for me.)
With a seam ripper, cut along the marked line to make a new hole in the inner layer of the waist. Be careful to not cut through the outer layer as well! And, make very tight Whip Stitches all the way around the hole that you just made. (If you do not want to sew, you can also apply fray stop glue around the edges of the hole.)
Remove one of the buttons from its original position and move it to the newly created opening. Sew the button onto the inner layer of the pants’ waist, approximately 1 cm or 3/8″ away from the opening in the direction of the front of the pants. (As shown above, it may help to insert a ruler or something similar to separate the two layers of the pants so that you don’t sew through both layers of the pants’ waist.)
If the existing adjustable waistband is not long enough to reach the new opening, you can extend it. (Make sure that the new strip of elastic that you will add also has button holes.) When sewing the new strip onto the existing waistband, make sure to overlap the ends of the two elastics by at least 2.5 cm (1″). And, sew them together by making stitches as shown by the green dotted lines in the photo above.
Attach a bodkin to one end of the elastic band, and insert it into the pants’ waist from the old opening. Then, push the adjustable elastic band through the pants’ waist until the tip of the bodkin reaches the new opening that you just made. Pull it out from there. Secure that end of the band by inserting the button through one of the elastic’s holes. Now you are finished with one side.
Repeat the same process with the other side of the pants, and you will have successfully taken in the already adjustable waist of your child’s pants!
If your child’s pants did not come with an adjustable waist band, then you may be interested in this tutorial for adding a new adjustable waistband onto them.