She replaces Beverley Hughes, who resigned earlier last week.
Ed Balls, who had been widely tipped to replace Alistair Darling asChancellor, is staying in his post as Secretary of State for Children,Schools and Families.
Ms Primarolo, who is MP for Bristol South, had been public healthminister since 2007.
She had held various Treasury posts since 1994 and was Paymaster Generalfrom 1999 to 2007.
Ms Primarolo, who recently took part in celebrations for the 3,000thchildren's centre opening, said she was delighted. 'I am looking forwardto driving forward policies that make a real difference to the support,advice and resources available to children and families,' she said.
Schools minister Jim Knight has moved to employment minister at Work andPensions.