Moms and dads often think their babies are wise beyond their weeks. Now, a study shows we may not even be giving the little ones enough credit: Babies can understand numbers and naturally associate small numbers with their left and large numbers with their right—even before they are 45 hours old.

How can scientists know this? After all, a baby who isn’t yet two days old isn’t exactly counting their little fingers. Well, the researchers out of Paris Descartes University conducted several tests by exposing 80 infants younger than 45 hours old to audio clips of repeating syllables, such as like “ba” or “ta.” Some of the babies heard six repeating sounds (representing the concept “few”) with others heard 18 repeating sounds (representing “many”).

Then the babies were shown geometric shapes. The babies who listened to the six repeating syllables saw a short rectangle, while the babies who heard 18 syllables saw a larger shape. Then the babies were played whichever repetition of syllables they hadn’t already been exposed to and where shown images of two shapes side by side.

According to the researchers, the babies who heard six syllables followed by 18 syllables looked at the right-hand rectangle twice as long as the left. The reverse was true of the babies who heard the 18 syllables first.

Complicated? Yes, but the results were clear to the researchers: Newborns have the ability to associate numbers.

Psychologist Maria Dolores de Hevia tells Science the parents she recruited were often surprised, too. She says, “It is a magic moment in which parents are aware for the first time of how receptive and attentive their newborn can be.”

Further research is needed with the researchers expressing curiosity with whether the findings would hold in cultures that read from the right to the left.

Either way, it’s proof that babies are way smarter—way earlier—than society gives them credit for. So parents aren’t totally nuts when they say an hours-old baby seems intelligent, even if they are a bit biased.