I took my daughter in December 03, when she was 5-1/2, and again in December 04, when she was 6-1/2, and she would have spent *hours* in the Boneyard, had I not insisted that we leave after, I think, about 30 or 40 minutes. My suggestion would be to time the Boneyard visit for a time when everyone needs some downtime and a rest, perhaps in the middle of the day, after lunch or something, and put a time limit on the duration. It's lots of fun for little ones, and if yours is like mine, they would rather play in the big sandbox than stand in line for some sort of thrill ride.
~YEKCIM