Jeans /trousers for a 'chunky' 13 yr old

[mckenzie]

i always used to buy DS's clothes from Next mainly but he's not slim build at all and their styles just don't fit him anymore.
He's Not tall, and quite chunky

Any ideas please as to where I might try?
TIA

Gap. My chunky 13 year old wore jeans from there till he stretched.