Kids clothing for slim children

[IDontLikeMondays88]

My little boy is tall but small around his waist so I am struggling to get clothes for him.
size 2-3 is now too short however size 3-4 is massive round his waist - actually falling down round his bum.
i think brand that sell a size 3 rather than 3-4 might be more suitable for him but the only shops I am aware to a size 3 are joules and gap. Can anyone give me any other suggestions?

@JackGrealishsLegs for school shorts try Sainsbury's Tu skinny fit classic grey school shorts they are £6. They have the adjustable waist and are far better than the M&S shorts, they are the only ones that fit my very slim 9 year old.

There is a brand called Name It which do very good super skinny jeans with adjustable waist which I first found in TK Maxx although I think Next and New Look might sell them and these are brilliant for slim kids and I think they do a girls range.

Thanks @beakyboo10!

I had a lot of good slim-cut things from La Redoute when DD was younger. Maybe worth a look.

Zara, Mango, Gap.
Boden is ok.