Two teenage siblings who were never allowed to attend school phoned the NSPCC to report their parents after Waltham Forest Council failed to intervene, a report has said.
The boy, 14, and his sister, 16, claimed they were "made to hide" when visitors came to their home.
The independent serious case review found social services could have acted sooner on 12 occasions.
Waltham Forest Council said there were "areas where improvements can be made".
It also emerged the parents had an older child, who is now 26, taken into care in 2001 due to allegations of neglect, according to the Local Democracy Reporting Service.
Despite the two younger children missing multiple medical appointments as babies and never enrolling in school, the report said social services did not seriously consider them "at risk".
The boy told the NSPCC call handler there were "secrets in the family" and that they "were confined to the house and allowed out to the park only outside school hours".
The teenagers were "pale and with their appearance suggestive of being malnourished" when found by police, who the report said had been notified by the NSPCC.
David Peplow, chair of Waltham Forest Council's Safeguarding Children Board, said the case had "highlighted issues of national concern" and "areas where improvements can be made".
The Met Police has launched a criminal investigation following the serious case review's findings.