Mary Cameron, 81, has put her name to a campaign against plans by Conservative-run Oxfordshire County Council to close a number of the centres, according to the Daily Mirror.
The BBC has seen a petition which shows the signature of Mary Cameron alongside her middle name and post code.
Downing Street declined to comment on the reports or the petition.
Retired magistrate, Mrs Cameron, told the newspaper: "My name is on the petition but I don't want to discuss this any further."
She reportedly signed the petition while visiting her son in Oxfordshire.
Oxfordshire County Council leader Ian Hudspeth refused to comment on Mrs Cameron's signing of the petition or the planned cuts.
Campaigners are trying to stop the closure of nearly all of Oxfordshire's 44 children's centres - the county council wants to keep eight hubs, to save Â£8m pounds.
The petition describes the proposals as a "false economy", and says the early intervention services provide numerous economic and other long-term benefits.
Campaign organiser Jill Huish said she was "not surprised" to have the Prime Minister's mother's endorsement.
"It shows how deep austerity is cutting our most vulnerable when even David Cameron's mum has had enough," she said.
"While our local authority and our prime minister squabble over who's fault it is that there are 95 separate cuts planned for Oxfordshire, we are the people who will suffer without our frontline services."
Council workers are to stage a 24-hour strike in protest at the plans.
The prime minister previously wrote to the local authority in his capacity as MP for Witney expressing "disappointment" at planned cuts to museums, libraries and day centres for the elderly.
But council leader Mr Hudspeth hit back, saying the cuts were the result of reductions in funding from central government.
Members of Unite employed in early intervention by Oxfordshire County Council will walk out on strike on February 16 after voting overwhelmingly for industrial action.
Unite regional officer Chris Gray said his members were "deeply committed" to the children and families they worked with.
"But they have decided that they cannot sit back and watch while the council denies Oxfordshire's young people a future and destroys its top class children's early intervention service."
David Cameron's mother has signed a petition against cuts to children's centres in his constituency.