Most children do not know how to build tension, their stories tend to jump from one point to the next or they tend to solve the problem too quickly and as a result the stories are not gripping.
I heard a creaking sound in the house. I wandered
downstairs and saw, to my horror, a masked man. He must be a burglar! I stood rooted to the ground, I was shaking with fear. The burglar suddenly turned and saw me. He advanced towards me and then he caught me and gagged me.
In the above example, the writing seems good in the sense that it has no grammar mistake and there is a smattering of good vocabulary used, however, as a reader, you are not gripped by the problem. The tension in the story is not built up, the burglar catches the main character too fast.
Here is another example of the same story but one where the tension is built up:
Creak..creak. What was that? I heard a strange creaking
sound come from the ground floor. There was no one else
at home. My parents had gone for a holiday. Was it a ghost,
a burglar or simply a stray cat?
Shivering, I tiptoed down the stairs. The hall and dining room
were dark and forbidding. Shadows loomed in the corners.
Just as I reached out to switch on the lights to dispel
the gloom, I heard the floorboard creak again.
Turning around, I saw a masked man advancing towards me.
Petrified, I stood rooted to ground, too frightened to move.
With a sneer on his face, the man came nearer and nearer.
I had to escape. I had to. I forced my trembling legs to move.
"Get back here!" the masked man threatened.
Without a backward glance, I ran up the stairs, slammed the
bedroom door shut and opened the window to call for help.
In this example, the tension is built by slowing increasing the intensity of the problems the character faces:
1) Heard a creaking noise
2) The character is alone at home and in a big house
– being alone makes it more scary for the character and being
in a big house makes the source of the sound harder to pin down,
you need some time before you discover who or what caused the
3) The rooms were dark and shadows loomed in the corners,
making the character more fearful
4) Just before the light is switched on, the creaking sound is
5) The character finally finds the source of the sound- the masked man
6) The masked man advances
7) The character bolts for the bedroom
At this point, the masked man has yet to catch the character. Unlike the other example, where the problem escalates too fast, here the intensity of the problem slowly increases, thus making it more gripping for the reader.
You can get your child to do this when he writes, get him to think of how he can increase the intensity of a problem slowly and write down the points of increasing intensity before writing his story.