Introduction Previous reviews of family-based interventions for childhood obesity treatment found that studies were of low methodological quality with inadequate details reported, especially related to intervention fidelity. The evaluation of fidelity is crucial to inform interpretation of the intervention outcomes. This study aimed to summarise intervention fidelity, participants’ acceptability and satisfaction with a 12-week family-focused technology-based child nutrition and weight management intervention. Methods Families with children aged 4–11 years participated in a telehealth intervention with complementary components: website, Facebook group and text messages. Intervention fidelity was reported using National Institutes of Health Treatment Fidelity Framework. Delivery was measured using a dietitian-reported evaluation survey. Google Analytics and Bitly platform were used to objectively track data on frequency and pattern of intervention use. Participants’ acceptability and satisfaction were measured using a process evaluation survey. Results Telehealth consultations delivered by trained dietitians had good adherence (≥83%) to the structured content. Process evaluation results indicated that parents ( n = 30; mean age 41 years, 97% were female, body mass index 30 kg/m²) found the intervention components easy to use/understand (87–100%), the programme had improved their family/child eating habits (93%), and they wanted to continue using telehealth and the website, as well as recommending it to other parents (90–91%). Discussion In summary, a family-focused technology-based child nutrition and weight management intervention using telehealth, website, Facebook and SMS can be delivered by trained dietitians with good fidelity and attain high acceptability and satisfaction among families with primary-school-aged children in New South Wales, Australia.