Sexual violence, especially sexual violence against children is very hard to study when it comes to the Holocaust. As to the last question, I would doubt guards would be punished, given how prevalent we think sexual violence may have been in such situations. Eli Wiesel's "Night" mentions that the sexual exploitation of boys by guards was an unspoken, but none the less accepted form of violence in Auschwitz. It is likely that this was similar in other camps, and we don't know if it was more or less acceptable for female guards. There are very very few testimonies of child survivors of sexual violence, or child witnesses of sexual violence during the Holocaust. The most common form of sexualized violence against children, mentioned with some frequency in survivor testimony, is the fact that boys suspected of being Jewish boys in hiding would be forced to pull down their pants to show soldiers whether or not they were circumcised. Sexual violence between prisoners during the Holocaust, whether pedophilic or otherwise, is an area of study which needs significantly more study. As you mentioned it is mostly found in rather vague anecdotes because it was an even more taboo subject for both survivor testimony and historical research. For much of the period since the Holocaust interviewers of survivors did not ask about sexualized violence, and when sexual violence was mentioned the survivors would often ask that this part of testimony not be included in the final interview. Because of this, and for many other reasons we have a serious lack of evidence regarding this, but in recent decades, researchers have come to believe that like in other genocides, sexual violence of all kinds was common during the Holocaust, and often went unpunished, especially when it was perpetrated by guards or German soldiers, or collaborator.