This article critically examines the legal arguments presented on behalf of Charlie Gard’s parents, Connie Yates and Chris Gard, based on a threshold test of significant harm for intervention into the decisions made jointly by holders of parental responsibility. It argues that the legal basis of the argument, from the case of Ashya King, was tenuous. It sought to introduce different categories of cases concerning children’s medical treatment when, despite the inevitable factual distinctions between individual cases, the duty of the judge in all cases to determine the best interests of the child is firmly established by the case law. It argues that the focus should not have been on a threshold for intervention but on whether his parents had established that the therapy they wanted was a viable alternative therapeutic option. In the April hearing, Charlie’s parents relied on the offer of treatment from a US doctor; by July they had an independent panel of international experts supporting their case although by this time the medical evidence was that it was too late for Charlie. One of Charlie’s legacies for future disputes may be that his case highlighted the need for evidence as to whether the treatment parents want for their child is a viable alternative therapeutic option before a court can determine which therapeutic option is in the best interests of the child.