A good tip for unusual and large size paper is paper table cloths. Often these are around 90cm x 90cm and ideal for bigger boxed gifts.
You can also find a really fab range of these paper cloths with unusual styles and colours. For children's gifts you can usually find a huge amount of themed and brightly coloured paper table cloths so you can go wild!
John Lewis does a great selection of paper cloths and you can find a huge selection on eBay.