1. Most likely the child is referring to a channel on a radio, such as a walkie talkie. What kids used before cell phones came out. 2. They are probably at the front door to an apartment building and the apartment that 'she' is in is upstairs on another floor. 3. Meaning that the person escaped a mental institution, left without permission. The gravity of the situation is that the person that escaped is unstable in some way and unpredictable. The first two answers depend a little bit on context so without seeing the shows those are my best answers.

Seems like some context is missing but I'll do my best using assumptions. 1) Do the characters have some sort of 2 way radio? Channel 5 would be the frequency the radio is using to communicate with others. 2) They would say come on UP if the visitor needs to go up stairs to their home. 3) An escapee is someone who has run away from some sort of imprisonment. In this case they are saying the subject has run away from a mental health facility (Nut house). When someone speaks of the "point" of their conversation they are referring to the main context or the main meaning of their words.