As the narrator informs us, Paul is small and built like his mother. (We're not really sure exactly what this means, but we're guessing we're supposed to think it's bad.)
He's pale and quiet, and seems old for his age. He hangs out with Annie a lot, who has turned into a tomboy by this point in the book. Nice.
That Paul's a weird one, though. One day, Paul burns Annie's doll, and seems to take some sort of sick pleasure in watching it melt and burn. This sounds like the kind of story that you hear about how serial killers spent their childhoods.
Anyway, like William and Annie, Paul dislikes his father. One day, he comes home and sees his mother with a swollen eye, and Walter standing nearby with his head down.
William tries to go after his dad, but his mom tells them that enough is enough for one night.
The family soon moves to a new house. It sits on a big hill, and the wind hits it very hard, giving it a spooky vibe. Cue horror film music here.
Now, the book really starts to speak of Paul and Mrs. Morel's relationship in disturbingly romantic terms.
When Paul brings his mother flowers, Mrs. Morel answers, "'Pretty!' […] in a curious tone, of a woman accepting a love-token" (4.149).
Mrs. Morel clearly loves William the most; but when William moves to Nottingham for work, she has no choice but to turn to Paul as her new closest companion.
That is, no choice if she's going to continue spending all her affection on her sons, thereby stunting their development, rather than on bettering her own relationship or life.
The children of Paul's neighborhood are very close, since there are so few of them. At night, they meet by the one lamppost on their street to play.
These days, Walter's hours at the pit aren't always great. He comes home in an ill temper when there's no work, and complains about how he's the only one in the family who isn't wasteful.
William moves away, and since he has to spend a lot of money when he first arrives at London, he can't send much home. Therefore, the Morels are even poorer that autumn.
William then comes home for five days that Christmas.
Like any young person totally unwise about money, William has spent every penny he has on Christmas presents. At least he's not selfish, right?
When he leaves, the family goes into mourning. Stuff is a lot more awkward without him, on the home front.
Later, William gets a chance to travel to the Mediterranean on his vacation, and his mother tells him to go. But he uses his vacation to come home instead, and she's secretly relieved and overjoyed by this.
Wow, Mrs. Morel: are you ever going to relax your vice grip on your sons' lives?
Given what seems to qualify as character development in this book—i.e., characters face the same problems over and over again and make little to no progress—we're not too hopeful.