Is It Only Me...Trouser Waistbands

My two boys are aged six and seven years old, and I have lots of difficulty finding trousers with adjustable waistbands - Most trousers from high street stores do not have adjustable waists with the exception to some High Street Stores - Next have a small range of trousers with adjustable waist then there's Sainsburys TU brand - I find these offer the best range but they sell out very fast, places like Primark only offer adjustable waist bands for 7-8 yrs but once you go into 8-9 age range forget it theres nothing available.
As we head into the new school term I always find myself on the hunt for suitable trousers.

Left- Blue Jeans by Next / Centre - Primark with belt no adjustable waistband / Right my favorite when it come to adjustable waist band -  Sainsburys TU range

Both my boys are getting taller and my seven almost eight yr old needs 8-9yrs,they both have slender waist bands and the standard sizes are just too big!!!! I dont want to spend a fortune on clothes my kids are going to wear to school (their school has a no uniform policy) I mainly shop online and catalogues such as Very also have a limited range.....How frustrating is it only me who has this problem.....!!!!