Background: Childhood obesity is an ongoing concern affecting many parents. Discussions around childhood obesity take place increasingly on social media, such as Internet discussion forums. On these platforms, parents present their experiences and apply cultural conceptions of childhood obesity. Argumentation on the platforms may affect how parents of children with obesity perceive obesity and adopt childhood obesity treatment. By exploring online discussions on childhood obesity, we can better understand the overall cultural conceptions concerning childhood obesity and the related responsibilities. This understanding may be used in health care to develop parents’ counselling for children’s weight issues. Method: We gathered and analysed 16 discussion threads on childhood obesity taken from a Finnish internet discussion forum, vauva.fi, between 2015 and 2021. In the analysis, we focused on threads where parents having a child with obesity took part. The data were analysed and interpreted with inductive thematic analysis.Results: In the online discussion on childhood obesity, the posts were mostly about the reasons and solutions for obesity, and obesity was discussed in the context of parental responsibility and lifestyle choices within the family. We located three themes that were used to define parenthood: being a good parent, being a bad parent, and being a blameless parent. Parents listed healthy elements in their family’s lifestyle to prove their good parenthood, whereas other commenters frequently tried to point out mistakes in the parents’ behaviour or offer advice. Moreover, many acknowledged that some factors causing childhood obesity were outside the parents’ influence. In addition, many parents were genuinely ignorant of the reasons for their child’s overweight. Conclusions: Our results showed that childhood obesity is not only a question of weight and lifestyle changes. Instead, defining parenthood and whether parents had fulfilled their tasks properly is the core issue. Consequently, counselling for parents in health care should be expanded from supporting a healthy lifestyle to strengthening parents’ identity as being good enough parents. Furthermore, efforts should be made to increase parents’ self-efficacy. In addition, supporting parents to accept and process feelings attached to the child’s weight would help them to manage in the present situation.