Actually, there is an organism on earth that is vaguely similar to the Russian dolls that you describe. The volvox:
Individual volvox cells, a kind of freshwater algae, reproduce in the conventional way (more or less), however, they also collect into spherical colonies (called volvocates, I think) with a tiny opening at one end. These spheres can reproduce by internal budding, with immature spheres growing within the body of the 'mother' sphere. Then at some point, the mother turns itself inside-out by inverting itself through the opening, releasing the 'daughter' spheres into the wild. The point where the daughter sphere connected with this interior of the mother becomes the opening of the daughter sphere (sort of like a navel in mammals). The cells that formerly composed the mother sphere don't simply die, however. Most of them are absorbed by one of the daughter spheres.
And yes, 'granddaughter' spheres can start to develop within the daughter spheres before 'birth'/'hatching'. In the following photo, you can see a mother colony in the process of disintegration, releasing it's daughters, which in turn have daughters already developing:
Photo credit: www.microscopy-uk.org.uk
Now, there are two differences between the volvox and your Russian dolls:
- The 'birth' event doesn't lead to complete death of the 'mother'.
- More than one daughter born per 'birth' event.
The first feature can be achieved by your dolls if the 'mother' dolls can reform somehow. Perhaps the 'head' can reattach to the 'tail' and continue living. After consuming enough nutrients from the environment, they could even begin the process of internal budding again. Or perhaps the daughters simply consume the mother's material, giving them a early boost in life.
The second feature can be achieved by simply dividing multiple times. Russian dolls have multiple layers inside at varying levels of size, but all are viable. When a large doll splits, a medium one emerges and splits, then a small one emerges and splits, then a smaller one, until there several offspring. Combined withe the above, you could have a burgeoning population of Russian dolls (Matryoshkavox?)