Do M&S school uniforms come small?

[Ethicaldebacle]

Our son is 5 and 8 months. He's fairly tall for his age (1.20m last time we checked) and looks ok weight wise. However, most of his trousers tend to be tight around the waistline, they fit slightly short length wise but they don't look ridiculously small. His jumpers/shirts all do look small. He's wearing size 6-7y

I've bought him a few size 8-9y and they seem to fit correctly (at least not huge).

So just wondered if it's my son or the clothes.

My DD was a month shy of 5 when she started school and was in size 3-4 M&S trousers, she’s only just gotten too tall for them now but they still fit round her waist. She’s 19kg and 110cm which I believe to be pretty average. I wouldn’t read into it too much - kids clothing sizes are as odd as all others!

It's just puzzling! Because another boy was wearing size 6 and they looked just fine (although my son is taller)