Children's versions of the Empathy Quotient (EQ-C) and Systemizing Quotient (SQ-C) were developed and administered to n = 1,256 parents of typically developing children, aged 4-11 years. Both measures showed good test-retest reliability and high internal consistency. As predicted, girls scored significantly higher on the EQ-C, and boys scored significantly higher on the SQ-C. A further sample of n = 265 children with Autism Spectrum Conditions (ASC) scored significantly lower on the EQ-C, and significantly higher on the SQ-C, compared to typical boys. Empathy and systemizing in children show similar patterns of sex differences to those observed in adults. Children with ASC tend towards a "hyper-masculinized" profile, irrespective of sex.