Quote 31
Beep beep, that's Door. Ma jumps up and makes a sound, I think she hit her head. She shuts Wardrobe tight. (1.410)
Ma's reaction to Old Nick's appearance is instant fear. It's incredible how much she manages to compose herself in his presence, given how frightening he is.
Quote 32
What if [Old Nick] comes and Ma won't wake up, will he be even more madder? Will he make worse marks on her? (2.153)
Jack is expressing quite a bit of empathy here. He's not afraid for just himself; he's afraid for Ma and her safety. That's very sensitive for a five-year-old.
Quote 33
Today I'm five. I was four last night going to sleep in Wardrobe, but when I wake up in Bed in the dark I'm changed to five, abracadabra. Before that I was three, then two, then one, then zero. "Was I minus numbers?" (1.1)
Jack understands a lot at five, but he still has a rough grasp of time. He doesn't yet understand that he is getting older every single day, not just magically clicking over from four to five on the night of his birthday.