The Children's Commissioner for England, Anne Longfield said her office would contact the head of children's services at the borough of Tower Hamlets.
It's after an investigation by The Times found a five year old girl from a Christian family had lived with two Muslim families in the last six months.
Anne Longfield was quoted by the newspaper as saying: "I am concerned at these reports. A child's religious, racial and cultural background should be taken into consideration when they are placed with foster carers."
It is alleged the youngster, who is white and a native English speaker, has wept and begged to return to her family because she doesn't understand Arabic.
Under the United Nations Convention on the Rights of the Child, a state fostering agency must recognise the "desirability of continuity in a child's upbringing and to the child's ethnic, religious, cultural and linguistic background."
The five year old girl claimed her necklace containing a Christian cross was taken away from her and she was prevented from eating Carbonara because it contains pork.
Speaking about the authority's fostering service, a Tower Hamlets council spokesman said: "In every case, we give absolute consideration to our children's background and cultural identity."