IMHO, if a kid chooses to and loves to follow instructions and build instead of free play with LEGO, let him/her. I don't think it would stifle creativity. That said, DD6 is like the pp's kids- she builds it once but immediately breaks it and mixes up all pieces. It used to drive me crazy as I did not like the idea of spending $$$ just to see it all mixed up. But I am cool about it now since dd has way more fun building her own stuff- she usually has a story in her head and builds around the story- it is pretty interesting. So now instead of spending money on sets, we go to the LEGO store and buy assorted bricks.
