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Something pure and simple like throwing a few dollar store army men and cowboys on the floor and playing with the kids for a good 1/2 hour to an hour can help brighten my weekends. Lately since my son is into Dawn of War and such we would throw some trio blocks on the floor and build up buildings, terrain and other obstacles the soldiers can hide behind for cover. It is a very primitive version of a playing actual Dawn of War tabletop game except it is more or less real time and there are no real rules as my four year old crashes through the toys with a dreadnought built out of Trio blocks.
Imagination is what is key and I often think back to the book and movie The Indian in the Cupboard and think how cool it would be if toys could be animated and you can literally engage in full scale recreations of battles and such with plastic figures. Sometimes I really miss being a kid and the next best thing is to just get on the floor and join your own kids in playing with toys.