Keeping your children in clothes that fit can be an expensive proposition. They can outgrow not only their clothes but your clothing budget faster then you expect. Knowing how to alter children's clothes waistbands will help you keep them in clothes that fit comfortably and keep you within budget. You can choose to purchase clothes a size or two larger then what they wear and take in the waistband or, let out the waistband of clothes that have become too small.
Mark the waistband with chalk where the button that is used to close the trousers should be moved to expand (or contract) the waist band. Do this while your child is wearing the trousers. Moving the button is only effective if you need to alter the waistband 1/2 inch or less.
Cut off the waistband button. Use the straight blade on the seam ripper to cut through the button thread holding it in place.
Sew the button in its new position by hand. Use "button thread," a very sturdy thread made for this purpose, in a colour that matches the original thread colour.
Pinch the waistband material together while your child is wearing the trousers so you can determine how much the waistband must be taken in. Measure the amount of material you gathered together in your pinch. For example, say your child's waistband needs to be contracted by 3 inches for a proper fit.
Use the seam ripper to remove the stitches on each side of the side seams and the back seam. You want to remove 5 inches to the side of each seam. Then, remove the 5 inches of stitches in the actual seams (going down the legs and rear of the trousers).
Cut the elastic waistband material in the waistband at each seam you just opened. If the trousers do not have elastics, cut the waistband at each seam so the seam areas are completely open.
Turn the trousers inside out. Make a diagonal chalk line at each seam, starting at the bottom of the seam where it is still sewn together and go towards the top so your diagonal chalk line is 1/3 of the amount that the trousers need to be taken in at the end (at the waistband). For example, if your child's waistband needs to be taken in 3 inches this means that each seam must be taken in 1 inch. Your diagonal line will start on the seam where it is still sewn and end 1 inch away from the old seam line at the top of the waistband.
Sew along the new seam line.
Iron the extra fabric of the seam flat against the inside of the trousers. Separate the two halves of the seam fabric so it looks like wings when you iron it down.
Overlap the elastic at the seam areas (where you cut the elastic earlier) so the elastic is neither lying loose or pulling on the waistband. (If your trousers do not have elastic, proceed to Step 8.) Sew the elastic in three places at each seam: the middle and both ends of the elastic pieces. Use a "Z" stitch when doing this. A "Z" stitch looks exactly like a "Z" with the top and bottom of the letter being stitches on each side of the seam joined by a diagonal. Most sewing machines have an automatic setting for this stitch.
Fold the waistband material over and sew it back in place.
Measure your child's waist with a fabric tape measure. The difference between the actual measurement and the size of your child's pant's waistband will tell you how much the waistband needs to be expanded. For example, your child may need the waistband expanded by 3 inches. This means the side and back seams must all expand 1 inch for the altered trousers to fit and look good (expand each seam 1/3 of the total measurement).
Rip the stitches out of the seams 5 inches to each side and 5 inches down the legs or rear of the trousers. Cut the elastic waistband material in this area (if there is no waistband material, cut the waistband itself).
Cut three triangles of your stretchable material that have a base that is equal to 1/3 of the total amount the trousers need to be expanded (in this example, 1 inch) plus 1/2 inch (your total base in this example would be 1 1/2 inches) and a height of 5 1/2 inches.
Pin your triangles into your side and back seams. Center the triangle so that 1/4 inch of the material overlaps the material of the trousers on each side. Sew the trousers material to the stretchable fabric. Use a double row of stitches where they overlap for strength.
Cut three pieces of elastic material 1/2 inch wider then the expanded amount at each seam. In this example, you will cut three pieces 1/2 inches in length. Sew the elastic pieces on to the old elastic so that 1/4 inch of the new piece overlap the old to join the two ends. Use a "Z" stitch when joining the elastic. If your waistband does not have elastic, skip this step and proceed to Step 6.
Cut three pieces of your matching waistband fabric 1/2 inch wider then the amount you expanded at each seam (in this example, cut them 1 1/2 inches wide) and twice the height of your waistband plus a 1/4 inch. For example, if the waistband was 1 inch tall, make your new fabric 2 1/4 inches tall.
Fold the waistband material over the elastic evenly and tuck 1/4 inch of the bottom and sides of the new material underneath itself. Pin this in place and sew along the bottom only. This way you will not "trap" the elastic and prevent it from stretching (if you have elastic in your waistband) but the bottom stitch will hold the fold on the sides of the material in place.
Use a button extender in a pinch. These are small elastics with a loop on one end and a button on the other. Place the loop over the waistband button and then use the button on the other end to close the trousers. This will expand the waistline by an inch or more immediately.