Big And Tall Cargo Shorts How Do I Expand A Child's Trousers Waistline For Comfortable Fit?

How do I expand a child's trousers waistline for comfortable fit? - big and tall cargo shorts

My child has special needs and is getting bigger and bigger around the waist with an alarming speed! It has a good, new pants, some brought from Next, and I want to extend the belt over it. They are the type of cargo pants, and most have a button asparagus, so I can not move to enlarge the size.

The straps are fixed, and sewing, but could not get in the cuff to expand, but as for the free movement, elastic waist, I have no idea? Can anyone advise all the way to do, thank you very much!