Anxiety disorders are common, debilitating, and begin early in life. Early intervention to prevent anxiety disorders in children who are at risk could have long-term impact. The 'Cool Little Kids' parenting group program has previously been shown to be efficacious in preventing anxiety disorders in temperamentally inhibited young children. Wider dissemination of the program could be achieved with an internet-based delivery platform, affording greater accessibility and convenience for parents. The aim of this study was to evaluate 'Cool Little Kids Online', a newly developed online version of the existing parenting group program. Fifty-one parents of children aged 3-6 years were recruited to evaluate the online program's acceptability and preliminary efficacy in reducing inhibited young children's anxiety problems. Parents were randomized to receive either a clinician-supported version or an unsupported version of the program. Parents had 10 weeks to access the program and completed questionnaires at baseline and post-intervention. Both groups showed medium-to-large reductions in children's anxiety symptoms, emotional symptoms, number of child anxiety diagnoses, and improvements in life interference from anxiety. The effect of clinician support was inconsistent and difficult to interpret. Parents reported high levels of satisfaction with the program. These encouraging results indicate that the online version is acceptable and useful for parents with temperamentally inhibited young children. Cool Little Kids Online may be a promising direction for improving access to an evidence-based prevention and early intervention program for child anxiety problems. A large randomized trial is warranted to further evaluate efficacy.