Decent fitting preschool trousers for small boy

[Hitchyhero]

I've just bought some from asda and they are way to long and way too baggy around the waist. I bought the elasticated one but it doesn't have any adjustable strap on the inside of the waist. My son in quite slim but I wouldn't say short. He's about 3.5 yo.

I've also tried a local shop that exclusively sells school wear and they instantly said we won't have anything that will fit.

Where can I find a good fitting pair of trousers. Any suggestions?

M&S long length means you can go down in the waist size but they will still be long enough.

I came on to say M&S too. My son is tiny weight wise but tall and is 4 in December.

Failing that, shorts!