strap not fitting small wrists

I want to buy an Apple watch series 3 for my son but the strap that comes with it does not fit his wrist. However, there is a strap on the accessories which is a Velcro based one (sport loop) which fits him very well. I think that paying £50 for strap that fits is not really acceptable.

Would Apple be able to exchange the strap it comes with for the one that fits on purchase? Or at least get a reasonable discount. The main issue is the strap that comes with the watch does not fit his wrist.

I feel Apple have not considered people with small wrists in this generation of smart watches. Although I know the series 5 (which is double the price of the Series 3) you can choose any strap.

I do feel that Apple are unfairly overcharging in this matter.