Parents have been urged to continue reading to their children even when they can fluently do so themselves.
It comes as research, published for World Book Day, found a fall in children and young people who say that they enjoy reading.
Over half of eight to 18-year-olds are reading for pleasure in 2019, down from 59% in 2016, the study for the National Literacy Trust said.
Only 26% are reading daily outside the classroom, compared with 43% in 2015.
Meanwhile, Nielsen Book Research's separate survey found that most parents stop reading to their children when they turn eight.
War Horse author Michael Morpurgo has backed a call for parents to continue reading to their children "well into their teens".
Experts say that being read to by a parent promotes independent reading.
Children's Laureate and author Lauren Child said: "Reading aloud with your child at any age is a wonderful way of connecting because you see what excites and interests them, and it's also a way of understanding what's going on inside their head.
"It's a lovely way of winding down at the end of a day for both parent and child. And it's letting them know by example that books are a good thing, creating a habit of reading and a special bond. For children, reading can be a gateway to learning but also to happiness."
Many primary schools across Wales encourage children to dress up for the day as a character from their favourite book.
Here are some pictures of some impressive costumes sent in from around the country.