Toddlers recognise basic arithmetic by the time they are 18-months-old, according to new research.
A team of scientists found infants of this age choose to watch videos that depict correct counting, rather than those where the sums do not add up.
The vast majority of human cultures possess a routine for counting things and although this generally is not mastered until children are about four, the study demonstrates the principles are first learned in infancy.
Professor Virginia Slaughter, of the University of Queensland, and colleagues said: "These findings demonstrate that humans begin to learn to count earlier than previously thought, based on exposure to their cultural counting routine."
The study involved a series of experiments in which infants viewed different videos depicting six fish, with the correct version featuring a hand pointing to each fish in turn accompanied by verbal counting up to six and the other a hand wrongly moving between just two of the six fish with the same commentary.
One test of 36 Australian infants found 18-month-olds, but not 15-month-olds, significantly preferred to watch the correct counting sequence.
Prof Slaughter said: "These results show infants start to acquire the abstract principles governing correct counting prior to producing any counting behaviour.
"Children begin to count some time after age two and their skill develops over the next several years. But before then, infants witness many instances of counting demonstrated by parents and older siblings, or portrayed on television.
"What, if anything, do very young children glean from this early exposure to counting?
"Our data suggest that between the ages of 15 and 18 months, infants begin to learn the abstract principles governing correct counting via exposure to their cultural counting routine.
"The preferential looking procedure we have developed offers a promising new direction for examining this issue further by revealing what infants learn about their cultural counting routine prior to producing the behaviour."
The findings were published in Proceedings of the Royal Society B.