Parents who reward their children's good behaviour with extra screen time can expect them to spend even more time online, warns new research - and may stop them learning social skills.

It's a well used modern day parenting hack, but a study suggests rewarding your child with extra time on their iPad for good behaviour may not be the best idea.

Researchers found children whose screen time is controlled as a reward or punishment spend more time stuck in front of a screen overall than those children who are not disciplined in that manner.

Scientists at the University of Guelph in Canada found children whose parents dole out screen time as a reward or revoke it as punishment spend more time on smartphones, tablets, computers or in front of the telly than kids whose parents don't.

Professor Jess Haines said: "It's similar to how we shouldn't use sugary treats as rewards because by doing so we can heighten the attraction to them.

"When you give food as a reward it makes children like the carrot less and the cake more. Same thing with screen time."

The study, published in the journal BMC Obesity, investigated the impact of parenting practices on the amount of time young children spend in front of screens.

The study involved 62 children between 18 months and five years of age, and 68 parents.

Lisa Tang, a PhD student who worked on the study, said: "We wanted to investigate the impact of parenting practices on toddler and preschooler's screen time because this is the age when habits and routines become established and they tend to continue throughout life.

"Also the use of mobile devices, such as tablets and smartphones, has soared in popularity among this age group in recent years."

As part of the study, parents were asked questions such as how they monitor their children's screen time, when children are allowed screen time and whether the parents spend time in front of a screen when around their children.

Results show that on average children spend nearly an hour and a half in front of a screen during weekdays and slightly more than two hours a day on weekends.

But with parents spending an average of two hours a day in front of a screen during the week and just over two-and-a-half hours a day on weekends it suggests children are learning from our example.

The study found a majority of parents use screen time as a way to control behaviour, especially on weekends. This resulted in children spending on average 20 minutes more a day on the weekend in front of a screen.

Prof Haines said: "We think the amount of screen time is higher on weekends because children are at home and typically have more interaction with their parents."

If parents spend time in front of a screen when around their children, the children also had higher amounts of screen time - which was more pronounced when the mother was the one spending time in front of a screen, according to the findings.

Prof Haines said: "It's possible the parent is allowing the child to be in front of a screen while they are.

"For parents of younger children, this isn't as common because parents can have their screen time while a child is napping or in bed.

"But as children get older, out-grow their naps and have later bedtimes, spending time in front of a screen without children around becomes more difficult."

Ms Tang added: "Watching screens takes away from other interactions that help children develop social and academic skills."