I'm with Dennis on this one... my understanding is the ACQ is good for play structures etc. and so would be fine for a sandbox. If you go with the ACQ treated wood, make sure you use hot-dip galvanized fasteners or the poly coated ones. Regular steel will not last long in treated wood.
Whatever you decide, build-your-own, or the little green and yellow plastic turtle, make sure you have and use a cover. Without the cover, you get:
- Debris (leaves, sticks, pine cones, etc.) to clean out
- Water
- Cats and other critters who will confuse the intended function of the sand
- Fleas
We found out about the last one with a sandbox in our yard. My son would often have little red welts from the knees down after playing in the sand.