Short Answer 
The Holocaust was the systematic genocide of over 6 million Jews by the Nazis during World War II, resulting in deep emotional trauma for survivors. Vulnerable groups, such as small children and older adults, faced increased risk of persecution, while the overall atmosphere was marked by pervasive fear and psychological strain among the Jewish population.
Step 1: Understanding the Holocaust
The Holocaust refers to the mass genocide of over 6 million Jews by the Nazis during World War II. This dark period in history saw the systematic extermination of Jewish communities across Europe. The term encompasses not only the physical destruction of a population but also the profound emotional and psychological trauma experienced by survivors and witnesses.
Step 2: Vulnerability of Specific Groups
During the Holocaust, certain groups, particularly small children and older adults, faced heightened vulnerability to Nazi persecution. Being part of these demographics often meant being selected for execution, due to prevalent racist ideologies and policies. Notably, the targeting of children extended to those with mental disabilities, as well as pregnant women, highlighting the brutal discrimination practiced by the Nazis.
Step 3: The Atmosphere of Fear
The overall atmosphere during the Holocaust was one of pervasive fear among Jewish populations. This fear stemmed from the constant threat of violence and death, causing immense psychological strain. In summary, this period was marked by confusion and terror, affecting both children and older adults as they grappled with the enormity of their persecution.