A totally representative group of about 200 American college students of child psychology were shown 60 chromatic photographs of infant faces: 5 male and 5 female each for six age levels (3, 5, 7, 9, 11, and 13 months). The babies were photographed by a professional photographer under controlled conditions when their facial expressions were judged to be relatively neutral, and the infants' shoulders were covered with a gray cape to hide clothing.
The study participants were instructed to rate the photos on a 5-point scale of cuteness (1: not very cute, 2: less cute than average, 3: average cuteness, 4: more cute than average, 5: very cute). The average rating was 2.75, ie somewhat less than averagely cute. The authors write that it's probably the selection of photos with neutral facial expressions and the grey cape which accounted for the students' overall perception as slightly less cute than average. And here's the plot of the results:
So, female cuteness peaks at 9 months.
For the above rating the participants were not told the gender of the child, but asked to guess it, which provided a 'perceived gender' assignment to each photo. In a second experiment, the participants were told a gender which however was randomly picked. It turned out that an infant perceived to be male but labeled female was perceived to be less cute than if it was labeled male. Thus the authors conclude that cuter infants are more likely to be perceived as female, and cuteness expectations are higher on females.
Partly related, Gloria just woke up: