The assertion that consciousness is a property of certain individuals and not
This is a very important and difficult question: how do we get from no consciousness to (our) consciousness? You've put the question in terms of ontogeny (or development), but the same sort of question arises in terms of phylogeny (or evolution)--which animals are conscious and which are not, and how did the latter evolve from the former?
The panpsychist alternative (b) may help, and it is advanced by contemporary philosophers such as Galen Strawson (and more tentatively, by David Chalmers). Despite that answer having to assert the seemingly weird claim that rocks have some sort of proto-conscious capacities, it is also unclear if panpsychism helps to answer the problem you raise, since we still need to know what organization of the proto-conscious material parts allows for the more complex consciousness we recognize in some animals and in humans. How do we get from paramecium (or blastocysts) made up of parts that have both physical and conscious properties to monkeys (or babies) that are made up of the same parts but organized in a way that clearly allows a sort of consciousness not shared by the paramecium and blastocysts?
There is no good answer to these questions yet, since we still lack a physicalist theory of consciousness--but when we have such a theory, the questions about development and evolution should become much less mysterious. For now, I think the best way to think about it is to recognize that consciousness comes in degrees and the jump from none to a very tiny bit may be no more mysterious than the vague jump from a non-heap to a heap, or the (less vague) state transitions from gas to liquid to solid or the transitions among species during evolution.
One reason the jump may look so radical may be a sort of illusion imposed by memory and/or self-awareness. When we transition from sleep state to conscious waking state (or from conscious to anesthetized unconsciousness), we don't notice a fuzzy boundary, but we may still go through one gradual transitions and simply be unable to be aware of them, remember them, or report on them. (Sorry if this bit sounds like a Dennettian evasion, but I think it's on the right track). Similarly, we can't easily get information from a newborn or fetus (or grasshopper?) about what it is like to be just a tiny bit conscious.
I hope this helps at least a tiny bit.