Bedtime stories are proving a struggle for many parents who are not confident readers, says a survey from adult learning agency Learndirect.
Parents and children benefit from reading together
More than 10% of the 1,000 parents asked had struggled to understand some words in the stories they had read to their five to 10-year-old children.
Parents said that they made up words they could not read or missed out difficult passages, the survey said.
Even more parents - a third - struggled with their children's maths homework.
Learndirect, which aims to improve the skills of adults, is producing a children's book, which it hopes will help both parents and children.
"When parents read to children they are physically close, giving all their attention to their children and sharing the experience of reading something they both enjoy," says child psychologist Pat Spungin.
"In this age of screen-based leisure, regular reading with young children can establish good long-term reading habits."
The problem of adults without basic literacy skills has been repeatedly highlighted - with employers warning of the damage to economic competitiveness.
A government-commissioned report into skills, published by Lord Leitch, called for a radical overhaul in adult training - and warned that the UK's skill base was lower than many international competitors.
The report said that five million adults lacked functional literacy and more than 17 million had difficulties with numbers.
More than one in six youngsters left school unable to read, write or add up properly, said the report.