Parents, take note! If you want your child to tell the truth, it may be best not to threaten to punish them if they lie.

Researchers from McGill University in Canada conducted a simple experiment involving 372 children between the ages of 4 and 8.

The researchers, led by Professor Victoria Talwar of McGill's Department of Educational and Counselling Psychology, left each child alone in a room for a minute with a toy behind them on a table, having told the child not to peek during their absence.

While they were out of the room, a hidden video camera filmed what went on.

When the researchers returned, they asked the child, a simple question: "When I was gone, did you turn around and peek at the toy?"

They found that 67.5 per cent or 251 children out of the 372 who were involved in the experiment peeked at the toy.

For every 1-month increase in age, children became slightly less likely to peek.

When the children were asked whether or not they had peeked, again 167 children or 66.5 per cent lied - and month-by-month as children aged, they both become more likely to tell lies and more adept at maintaining their lies.

The researchers also found that children were less likely to tell the truth if they were afraid of being punished than if they were asked to tell the truth either because it would please the adult, or because it was the right thing to do and would make the child feel good.

The study found that while younger children were more focused on telling the truth to please the adults, the older children had better internalised standards of behaviour which made them tell the truth because it was the right thing to do.

"The bottom line is that punishment does not promote truth-telling," said Talwar.

"In fact, the threat of punishment can have the reverse effect by reducing the likelihood that children will tell the truth when encouraged to do so.

"This is useful information for all parents of young children and for the professionals like teachers who work with them and want to encourage young children to be honest," Talwar said.