Star Children

System of A Down "Aerials in the Sky"

The term Star Child is thrown around nowadays be a number of individuals. Many of these are abductees or individuals who have had a Close Encounter. Many often feel out of touch with humanity, feel a sense of not fitting in, have a higher conscious, feel intellectually superior, feel spiritually concerned, need to feel special, Eco-friendly,  who feel in tune with the cosmic awareness, possessed by an alien intelligence, watched by the government....etc.
There are many reasons why someone may feel they are Star Children...... usually those individuals are on more friendly terms with the alien visitors.

One of the origins of this phrase comes from stories attributed to the Native Americans of the Southwest of the U.S.A. Apparently the Hopi new of these Star Beings. Basically from time to time, as it was custom with some tribes....you exchange children to foster trust with eachother as a cultural exchange. These beings hosted by the Native Americans were dubbed "Star Children".

This is not an official classification of the subject, but what I have put together based off of my research.
There are two types of Star Children....Physical Star Children which are biological constructs/lifeforms and Mental Star Children which deal more with a psychological and spiritual aspect..
 
Physical Star Children

Altered Human
For whatever reason a human, through mental manipulation or physical mutation can be a "Star child". This is usually the beginning stage. Abductee could be introduced to the aliens culture and mindset. Just the very act of constant abductions make them "Star Children", as they become more and more familiar.
Physically "Star Children" can also occur through a physical means. Small alteration in the genetic make up are made so they become more compatible with other types of Hybrids, Breeding Programs, or adaptivity for technological or environmental purposes.

Genetically Altered Being
This "Star Child" has been genetically altered to resemble the physical make-up of the host species. In essence the original species goes through gene therapy in which the existing DNA patterns are overwritten. With someone who is close to you it is a minor alteration overall, however the larger the gap the more tricky it can be.
Once the Genetic Sequence has been rewritten these being can be re-introduced into society.
These Star Children can be adult versions or embryos implanted in human hosts.

Cloned
Since we are dealing with a species with advanced technology, they may have access to clone and a stable genetic matrix. What happens a stock individual is cloned. The original individual can be "kept somewhere" or be allowed to return. The clone operates as the individual, but has been usual conditioned to be more receptive if in close contact with the alien. However clones are usually operated like our Flashdrives, were data/memory are uploaded, examined, and monitored. What can be more challenging is the series of clones can be re-integrated through the link of society.
This could explain past-life experiences, as our clones previous memories have been accidentally transferred to the latest batch. Also if more than one clone is in operation or if the original model is aware, they may be accidentally sharing memories as they will have very similar brainwaves. Its like feedback in away.   
A contemporary example is the movie Avatar, where a cloned individual is made and controlled by is a host intelligence. However in the case above, these are a series of clones like the Vorta from Star Trek DS9.

Hybrid
These versions of "Star children" come in various models depending on the generations of crossbreeding. A Stage I Hybrids will have traits of the dominate gene pool. Most cross-species breeding will produce mutants, malformed, sterile, or still born lifeforms in the beginning. Depending on the programs success there can be a number of generational models.
Some models may have certain desired traits, and kept in production while the True Hybrid is perfected.
With enough adaptions a stable new lifeform can eventually be formed, a True hybrid. These lifeforms would be of a new species, and may not be compatible with the original stock species.

The life of this type of "Star Child" is difficult, as it will be different from both of its stock parents. Most Hybrids are never introduced into our society. Those that are later generation models that are stable and are manipulated into contact with other hybrids. Late generation hybrids often have cosmetic surgery to better integrate themselves into society. Most may be unaware that they are hybrids.

Mental Star Children

Host
some would consider this a possession. This is when an alien consciousness takes over you mind for a period of time. Your consciousness could be suppressed in which missing time is experienced or is just along for the ride. In some cases you may not be aware, as it acts as a suppressed state just watching through your eyes. This can be duplicated by a technological means.

Soul Swapped
Although some may call it "Mind Swapping", this category of the "Star Children" is what I would considered a person who essence/soul/mind and has been transferred out of their body.
They could be transferred to another cloned body, synthoid, alien body. Their body however is know the host to an alien conscious for a time. This could be mistaken as possession.
In contemporary media this is illustrated by H.P. Lovecrafts, "Great Race of Yith" in 1936 and in the TV series Stargate Universe and Stargate SG-1 with the communication Stones.

Imprinted
If Mind Swapping has occurred too frequently, either alien or host may biologically retain the new synapse configuration in the brain. What this means, is that either one will have hard copied memories of the other. This may lead some to erroneous believe that they are a "Star Child" or alien trapped in a human vessel.
This can be seen in computers, sometime certain types of data copied on to your hard drive will become permanent fixtures. As any tech will tell you things are never really deleted from you hard drive, and like our brain our memories are hard copied too...it just a matter of accessing them.

Soul Merged
Soul Merged, is when the essence/soul/mind of an alien consciousness if fully integrated into that of the human. This can be done intentionally in order for alien to experience life through the eyes of the host, making them an instant "Star Child". The main issue is the blending of two consciousness. Children make the most malleable subjects as their mind are not fully formed. Adults however provide more difficulty as their personality/ids/ego will conflict with the additional developed consciousness. Willing adults who surrender themselves would have an easier time adjusting. When its mission is complete it can choose to live out its life here, return, or be recalled back (Abduction with no coming back).

Examples are the Goa'uld from Stargate SG-1 and the Trill from Star Trek the Next Generation and DS9. Although both of these examples have a biological entity inserted into the host, they both bound with each other becoming one lifeform. Both however have the abilty to outlive the host and transfer to another lifeform.