Introduction Innovative eHealth solutions that improve access to child weight management interventions are crucial to address the rising prevalence of childhood obesity globally. The study aimed to evaluate the feasibility and preliminary efficacy of a 12-week online telehealth nutrition intervention to improve child weight and dietary outcomes, and the impact of additional text messages (SMS) targeted to mothers and fathers. Methods Families with children aged 4 to 11 were randomised across three groups: Telehealth, Telehealth+SMS, or Waitlist control. Telehealth and Telehealth+SMS groups received two telehealth consultations delivered by a dietitian, 12 weeks access to a nutrition website and a private Facebook group. The Telehealth+SMS group received additional SMS. Feasibility was assessed through recruitment, retention, and intervention utilisation. Efficacy was assessed through changes in measured child body mass index (BMI), waist circumference and diet. Results Forty-four (96%) and 36 (78%) families attended initial and second telehealth consultations, respectively. Thirty-six families (78%) completed week 12 assessments. Child BMI and waist circumference changes from baseline to week 12 were not statistically different within or between groups. Children in Telehealth+SMS had significantly reduced percentage energy from energy-dense nutrient-poor food (95% CI −21.99 to −0.03%E; p = .038) and increased percentage energy from healthy core food (95% CI −0.21 to 21.89%E; p = .045) compared to Waitlist control. Discussion A family-focused online telehealth nutrition intervention is feasible. While the modest sample size reduced power to detect between-group changes in weight status, some improvements in child dietary intakes were identified in those receiving telehealth and SMS.