Trousers for DS with a slightly larger derrière (posterior);

[Tigerzmum]

My DS has a prominent, well-shaped posterior; -hence literally all of his trousers are prone to split in the crotch region; Please, please can anyone advise on shops which cater for this in the cut of their trousers; otherwise, he is a normal leg length of 32" and waist 32"; The usual high street shops cater for an average fitting.

You have my sympathy!
My DS(24) has had similar issues with trousers and tends to avoid them whenever possible. Drop crotch joggers are the perfect shape and he's dreading the day that he can no longer buy them, they're only online these days as they're no longer high fashion.
He happened upon a cut of jeans with stretch that fit well from Next, he's been wearing them in black as an alternative to trousers while the office has temporarily relaxed their dress code.
His best fitting 'proper' trousers are actually pleat front 'classic' style- as he's got huge thighs too they don't look like old mans trousers on him.
Places like Matalan, M&S and Sainsbury's yielded far better results than any of the young fashion shops.

DS is not at all fat but going through a slightly 'solid' stage in early teens which I think is a result of him not growing upwards yet! He is wearing quite a lot of M and S both in jeans and school trousers. Really nice jeans with lots of choice there - and school trousers that are for his cut which have some awful name like 'bigger fit' but they are great and fit his rather roundish bottom very well!

My son is much more stocky nowadays with the kind of backside reality stars pay for. We find Tesco school trousers excellent.

My son is like this! He's inherited my well cushioned bum!! I have noticed that his age 12-13 (he's 10!) M&S school shorts are gapping at the pockets because of this.
I have just bought his some next jeans that look nice.