We do a stocking (felt sack with their name on) at the end of their bed, left by Father Christmas. That usually has about 10 small presents in it - annual, small game, satsuma, sweets, comic, footy cards etc they open that upstairs in our room and then we all go downstairs to see what Father Christmas has also left under the tree
This is usually 3 or 4 bigger presents - i.e dolls house, bike, pushchair, PS3 game
We always did it this way ourselves a kids and draws the whole process out a bit. Otherwise its over in a few minutes. We also have a stocking each ourselves as we are big kids
The other thing i do to make it special is make "magic father Christmas snow prints " on the carpet with a boot as a template and shaking icing sugar from a sieve. I have them leading from the fireplace to the tree