Referring to objects as young children look at them gives them a clue about the meaning of the word and helps their development of language.
Up to a quarter of the difference between children's vocabularies when they enter kindergarten could be down to how well their parents use "non-verbal cues" when talking to them, researchers said.
Saying "There goes the zebra" whilst visiting a zoo, for example, is more helpful to a child than simply saying "Let's go to see the zebra" and will help a child learn the animal's name faster.
Researchers from the University of Chicago filmed 50 parents and their children, who were aged 14 to 18 months, during the course of a normal day and studied the video footage.
Some parents provided clues about 38 per cent of unfamiliar words they used, for example by referring to something the child was looking at, but in other cases the figure was just five per cent.
The findings, published in the Proceedings of the National Academy of Sciences journal, showed that differences in the parents' use of visual clues could account for 22 per cent of the differences in children's linguistic ability when they reached kindergarten.
Dr Erica Cartmill, who led the research, said: "Children's vocabularies vary greatly in size by the time they enter school. "Because preschool vocabulary is a major predictor of subsequent school success, this variability must be taken seriously and its sources understood."