Do the boys like playing football, or do they support a particular team? If they support a certain team then you could always pick something up that is related to the club they support. If it is a really popular club, or the local team then you should be able to pick something up in the town centre, if not then you can always look on the internet for the club shop of the team they support.
For the girl you could go to somewhere like Hobbycraft and pick up a jewellery making kit.
Gift vouchers for the 15 year old girl for shops like New Look,gadget of some sort for the 16 year old boy,computer or console game for the 10 year old.