This store is great for kids and adults alike. It's almost the exact opposite of big chain stores - they have some flashy toys, but many of them are just old-fashioned fun. Great Turtle has many toys out of the boxes to play with, too.
Great Turtle's biggest and best area is kites. They have tons of them, and many accessories: string, bows, and anything else you can imagine. When we visited Mackinac, they had a group out along the beach doing a kite demonstration.
Great Turtle is off the main stretch of shops, but it's worth the 10-minute walk. If you visit the website, they have a discount coupon.