I just watched this video on Liam Hoekstra at 3 years old
So maybe I don't have a good idea of what 3-year-olds can do, but the feats in that video don't seem earth-shattering, nor does his physique look out of the ordinary. They said he did inverted sit-ups, then on video he does normal sit-ups.
I'm totally calling BS on the iron cross at 19 months old. Show it on video, especially now that he's ~3 years old!
Oh yes, the other parts in the myostatin page that Gant linked. Imagine that, an "unusually strong" parent(s) having "unusually strong" offspring. Sheesh.
It would seem that the power-to-weight ratio and the leverage of muscle fibers of these myostatin-deficient folks doesn't seem to pan out as well as people think once they are adults
. Maybe it's only good for BBing purposes...