We separated our Legos recently. Tuck's routine had been to build a new set following the instructions, and then immediately take it apart, dump the pieces into a huge tub with all of his other Legos, and begin to combine the parts in new ways.
Tolliver, on the other hand, is currently really keen on building and rebuilding Lego guys. So we sorted all the small people parts into a special container. He spends hours a day making characters whose legs and arms change regularly, who wear handcuffs and hats and goggles and braids. He creates zombies and ancient egyptians and goblins and farmers, and he keeps them all busy driving vehicles Tucker has assembled and tending structures Tucker creates. It's turning out to be a pretty good partnership.