So in the 1861 Census in Cornwall - there is a family that might be the ones you want.
They are living in Vyvian Row in Parish of Camborne, Cornwall, and all born in Camborne
George Rowe, Head, married, age 40, Blacksmith
Mary Ann Rowe, wife, age 37
Thomas Pearce, son in law, age 17, unmarried, Miner
Charles Davey Pearce, son in law, age 14, Miner
Elizth Jane Pearce, daughter in law, age 11, Scholar
James Rowe, son, age 9, Scholar
Mary Ann Pearce, daughter in law, age 8, Scholar.
My reading of this would be that James is son of George by a previous marriage, and the Pearce children are the children of Mary Ann by a previous marriage and George's step children. Cornwall OPC does have children by this name baptised in Camborne, children of William and Mary Ann Pearce.
Couldn't find a marriage for George Rowe and Mary Ann Pearce in Cornwall OPC, but in FreeBMD there is a marriage registered in Dec 1855 in Redruth District (Camborne is in this district) between George Rowe and Mary Ann Pearse
It wouldn't be the first time that someone filling in a death certificate has got confused on some of the details and Pearce was the surname of his James, step-mother not his mother?