Jacobus Newhouse's favourite non-fiction topic is "the universe, cosmos and space" but when the nine-year-old struggles to sleep at night, he reads fiction to relax.

The Illawarra Grammar School student has encouraged other children to put down the console and pick up a book on International Children's Book Day on Wednesday.

"Why wouldn't anyone read?" he said.

Although he has watched documentaries about space, the year 3 student attributes his in-depth knowledge of the universe to reading.

"About 85 to 90 per cent of my knowledge about it comes from books," he said.

"Neptune is my favourite planet because it's the furthest major planet from the sun and I like its blue colour."

The student's passion for prose has extended to writing mini-books about space.

"I would get a texta and write it. The last book was called Planets," he said.

The school's teaching and learning co-ordinator Karen Wallace said Jacobus was naturally inquisitive.