This paper examines some spectral features of voiceless fricatives /s, ʃ, f, θ/ produced by Australian English-speaking children (5-13 years). It finds that sex differences are evident in fricative production, despite the unlikelihood of sex dimorphism in the vocal tract. These differences are especially evident in the sibilant fricatives /s/ and /ʃ/. Girls produce sibilants with higher spectral mean and lower spectral skewness than boys. Boys produce /f/ with a higher spectral mean and lower skewness than girls, while spectral mean and skewness for /θ/ are very similar between sexes. Spectral mean of /s, ʃ/ and /f/ declines significantly with age, while /θ/ shows no change. This work builds upon our current knowledge of sociophonetic variation in Australian English, as well as our knowledge of children’s acquisition and use of socially-structured variation.