In case I did not already love our local public library, they had a free LEGO day last week. We went with some friends of ours. I suggested they go because the kids can play with toys and make a huge mess "somewhere other than your house!"
The event was only an hour, but could have lasted for several hours. It could not be simpler. They had all the kids sit at tables and gave each table big piles of LEGOS.
Tons of fun!