Okay kiddo, so an indictment is when a group of people (usually lawyers called a grand jury) look at a lot of evidence and decide if someone should be charged with a crime.
Now, the McMartin Trial is a famous case that happened a long time ago. It was a trial in the United States where seven people who worked at a daycare center were accused of hurting children who were in their care.
The case was very complicated because the children said a lot of different things and some of the evidence didn't make sense. Eventually, the grand jury decided to indict the people who worked at the daycare, which means they thought there was enough evidence to charge them with a crime.
But the trial went on for a long time and some people didn't agree with the grand jury's decision. In the end, some of the people were found not guilty and the others had their charges dropped. It was a sad and confusing time for everyone involved.