Hi Jaye,
A 1.5mm Akoya pearl would most likely be a keshi, with its baroque shape, a by-product of the culturing process. Seems to me like calling it a "baby" is just a way enhance desirability. High quality keshi, from mussel or oyster are very desirable. Exactly how rare is difficult to say. I'm not aware of Akoya pearls that size with a bead inside. Please tell us more!