Verify that the general conditions are met that allow you to reliably use the hypothesis test. 

However, note that we do not have enough information to be certain if the condition "the observations are independent" is met.  The study paper states there was a sample of infants, and we can assume the observations are independent.  The only obvious way that would not be the case is if there were twins (or triplets...) in the study, which we can assume was not the case.