I guess this is one of those areas where different theories of understanding child development, trauma and recovery will really inform your understanding of how people go on to recover, or to develop PTSD.
So, children are inherently more resilient because their understanding and way of being in the world are still developing. Attachment theory suggests that early trauma may affect early attachment which then creates an internal working model that the world is unsafe (
@EveHarrington'a cracked foundation if you will). Some children go on to overcome the early trauma because there are enough factors to promote their inherent resilience e.g. secure family relationships, a sense of self efficacy, mastery etc. In such cases the early experience of trauma can protect against PTSD in adulthood because as a child they learned that the world can be unsafe, but that they are able to come through that and survive.
Early trauma in a continuing adverse environment means the child never gets the opportunity to process their experiences in safe, caring relationships and their inherent resilience continues to be undermined. Such children then struggle with adult traumatic experiences because they don't have a secure foundation to hold themselves. They may have built up defences, look entirely functional but the structure crumbles in the face of adult experiences which are overwhelming to their fairly fragile sense of self.
Adults who grew up in secure environments who experience trauma as an adult often show much stronger initial traumatic responses but bounce back more quickly because they have a solid place to work from, and to return too once the initial shock has been worked through.
That's just one model, there are many different ways of understanding trauma which each say slightly different things. None, I think, have it entirely pegged because child development is complex, the way we respond to trauma is complex and the human psyche is complex.
