Probably not the same species. Count the ribs. The small appears to have far more than the large one. It is unlikely to lose them as it matures so probably a different species.

One possibility for the baby is Stenocactus pentacanthus but its hard to be sure at this age. S. pentacanthus is quite striking when mature, with very long central spines. It is considered a form of S. obvallatus which has more normal central spines.