My boys absolutely love going to the Home Depot and Lowe's kids workshops and both stores are hosting them this weekend (both obviously focusing on Mother's Day):
At Lowe's your kids can make a flower vase. You can register before hand or show up right at 10:00 to make sure there are enough kits for your kiddos. The clinic lasts until noon and is recommended for kids ages 5-12, though we've taken both of our boys and at ages 2 and 4 they enjoy it a lot!
Have your kids make a Tulip Planter at Home Depot. You just show up between 9:00 and noon to build it. Last time we went, there were brownies, popcorn and balloons as well, though I don't know if this is common :). You may want to call ahead to make sure your store is participating.