RecruitingPhase 2Drug trialTreatment of Social and Language Deficits With Leucovorin for Young Children With AutismThe primary objective of this study is to evaluate the cognitive and behavioral effects of liquid leucovorin calcium on young children with autism spectrum disorder (ASD) and determine whether it improves social communication as well as the core and associated symptoms of ASD. The investigators will enroll 80 children across two sites, between the ages of 2.5 and 5 years, with confirmed ASD and known social and communication delays. Participation will last approximately 26 weeks, from screening visit to end of treatment.