What are some fun things that kids 12 and under can do ?

Take them shoplifting.  It may be that they are under the age of criminal responsibility, and you can allow them to pick their own Christmas presents without fear of arrest.

When I was their age I saw everything a magazine would show us to make it in life.

Oh, so now we have to do the work of your utter lack of imagination?  What's in it for us?  Were you never under 12?  What did you do?  

Get some plastic gold pans.  Go out and pan for gold.  It does not matter where,  just do it.    

Get a metal detector.   Each time it beeps,  have one kid do some digging.  

Collect garbage along a hiking trail. 

Do geocaching.   Look it up.  

The idea is do stuff OUT SIDE and way from other people.  

Play in the sprinkler, play hide n seek, watch ET, bake a cake together, wash the car, play baseball, play video games, make their own comic strips, color, build with blocks, read, play shadow puppets, make new hair styles with mousse, draw hop scotch with chalk, collect bugs in plastic cups they hunted up in the yard and make a zoo, make a fort, collect leaves, make mud pies, find flowers in the yard, ride bikes, make a 'menu and open a restruant, make a band with pots and pans, 

The list is endless. Why not start some craftwork that you will be able to carry on into adult hood? I began cross-stictching at the age of 9 and now, at 33, I can do really fine, split stitch embroidery, Ruskin lace, white work etc - a whole range of decorative stitching..