This question reflects the confusion with the term trauma that is so pervasive. People call “trauma” to traumatic events but not every traumatic event causes trauma. Trauma means “wound,” and I explain it using an analogy:
Trauma is equivalent to a “cut on your skin made by a knife.” Trauma is not the knife.
The difference is that the injury or cut is not in a surface, but in your nervous system. And the knife is the abuse or neglect, or the event that made you feel unsafe and at risk. Like the knife, it could cut you or could not. It depends on several factors.
Developmental trauma means that the wound or traumatic injury occurred when the brain was developing, which could include the first 20–25 years of your life. It’s important to make this distinction because the damage that traumatization causes in a developing brain has more severe consequences than if the brain has already matured. And if we don’t know this, we may not put extra effort into preventing this damage to occur.
We actually don’t have any preventive measures for Developmental Trauma since it’s not officially recognized, and therefore, there is no effort to prevent it.
Here is an explanation of what Developmental Trauma disorder (DTD) could look like if approved: What is developmental trauma disorder?
To respond to your question, neglect would be the knife, and developmental trauma would be the wound that the knife causes when used to injure the child constantly and prolonged. It may not be a strong stabbing that could immediately be a life threat (and that would cause PTSD), but a cut that keeps going deeper and deeper, or maybe just scratches the surface until there is such a large surface wounded that the slow bleeding finally reaches a point where the person starts suffering from anemia. In the case of DTD is not anemia, but a bunch of symptoms that represent the alterations that the nervous system finally suffers from.
The neglect keeps the child in a state of high stress and that stress activates a system called Allostasis. Allostasis makes small changes in the functioning of the nervous system to maintain homeostasis until it reaches a point when it can’t continue making small changes because the accumulation of changes reaches the point of something called Allostatic Load.
At that moment, the system “breaks”. When that happens it means that the system can’t take it anymore and loses homeostasis, which means that the alterations may become more permanent and the system will operate in an unbalanced way. Then all sorts of symptoms develop as manifestations of that lack of equilibrium, and the system would be traumatized. The child suffers from then on of Developmental Trauma Disorder and his/her brain will be damaged because the traumatization would block the healthy development of functions and brain parts.