I'm not sure that the "child's fist" is an SI unit, so I'm not entirely sure what to make of that
A single head of even the largest Lithops species is abnormal if it is bigger than a couple of inches across. Some species will form big clumps though, bigger than my fist, let alone a child. Or you can stack up a single head and make quite a large "lump". I've seen them fill a dish a foot wide.
Although Lithops will naturally grow with little (or nothing!) showing above ground, when treated generously in poor light they can elongate so several inches tall. Combine that with being pampered to a couple of inches across and you can get a substantial amount of Lithops.
Then there are the little species that most people will never see for sale, single heads always less than an inch. Oten they stay single, but sometimes they clump up too. L. dinteri and L. werneri are both very small, but will make clumps of 20 heads very easily. L. divergens has equally tiny heads, although they spread themselves out to look big, and it prefers to stay single.
My advice is not to buy over-fed over-fat Lithops. They will die at the slightest provocation, or at no provocation at all. Colour is usually poor through lack of light and too much food.
L. viridis seedlings often show this reddish shade, but never seem to produce convincing red adults.
