Feltham is divided into two parts, Feltham A holds children and young people, mostly aged 16 or 17, while Feltham B holds young adult men aged 18 to 21.
Chief Inspector of Prisons Nick Hardwick said:
"Feltham as a whole is an unacceptably violent place. Despite excellent work in some cases, staff were unable to prevent a high number of very concerning incidents that carried a significant risk of serious injury.
"In my view staff were sometimes overwhelmed by the challenges they faced and as a consequence, some of their response, such as the prolonged use of isolation on the children and young people's side and the use of batons on the young adult side, were unacceptable."
Mr Hardwick found that Feltham needed to rethink its role and cautiously welcomed a decision taken after the inspection to not hold young adults on remand as this may help to create a more stable and manageable population.
Elsewhere, the inspection found that many young people said they were frightened at the time of the inspection and had little confidence in staff to keep them safe.
More top news
Several famous London landmarks lost their illuminations for an hour last night as part of a charity campaign to highlight climate change.
As Christians communities prepare to mark Holy Week, find out the true meaning behind the Easter story and how each day will be celebrated.
More than 200 people are expected at London's first Muslim Youth Festival which will look at stopping the radicalisation of young Britons.