Bought two 8" twins for bunkbeds. Although the bunkbeds recommended 6" mattresses, all the reviews indicated that the expansion isn't 8" but somewhere between 5"-8". Those reviews are all spot-on, mine expanded around 5". I have 7" spaces in between bunkbed slats and the mattresses fit in there perfectly with just a little room either at the bottom or head of the bed. The mattresses do not fall through the slat openings, they lay "on top" of them just fine. I laid on the mattresses and they are actually very comfortable. I had read reviews that folks could feel the slats or springs and even though I'm overweight, I did not have that issue. They should be perfect for children! If you're using these on bunkbeds, I recommend going up to the next size in thickness since they really do not expand 8".  I think these mattresses are a great buy for the money and they are really pretty and comfortable. I would purchase again!