What constitutes good or bad writing is subjective because, from a reader's viewpoint, what we like and dislike varies greatly. Despite this, there are ways of writing that will usually be considered poor. To demonstrate this, I'm delighted to share the words of my grandson, aged five, when forced to endure 'take home readers'.
Though not particularly fast in learning to read, Master Five valued story and longed to be able to read things himself. Despite this longing, the pleasure of deciphering a narrative was eroded away as he came to uncover lots of repetition. He found early readers so boring he resented having to slog through them.
One particular day, reading to Pa, he stopped part way through a text to declare, 'The person who wrote this has made lots of mistakes.'
'No they haven't,' said Pa. 'Keep reading.'
'But it's wrong,' came the answer.
The story was about an old man who gained social interaction by spending time near his front gate. Each time a different person passed by, they greeted him.
'Tell Pa what exactly is wrong,' I said. I wasn't sure what was coming.
'Okay, listen.' Master Five began reading. 'The post man arrived. Good morning, Mr Jones, said the post man.'
'That's right,' said Pa.
'No, it's not,' came the reply. 'It says the post man arrived, so when he says, Good morning, Mr Jones, it shouldn't say said the post man. Of course it was the post man who said it. That's who just arrived.'
'Well, that's not exactly wrong,' said Pa.
'Fine,' said Master Five. 'Technically it's not wrong.' (Yes, kids of five use this wording.) 'But if you want to say that someone said it, you don't need to say said the post man. You just say, he said.'
Noticing Master Five gritting his teeth as he conceded this, I said, 'You are right. I guess what we need to remember is that because this sort of story is written to help us learn to read, it repeats some words so that we become familiar with them.'
'Well, that means it's worse than boring,' came the answer. 'It's just bad writing.'
On the inside, I was cheering. See, while this is the kind of example I'd use to demonstrate poor writing, he doesn't hear me talking about this. He's concluded this by himself because he's been exposed to good writing ever since he was read to.
So, if you write for kids, never resort to writing poorly. Get rid of unnecessary words and only use that repetitive style for when publishers ask you to write specifically for the 'take home reader' market.