The International Genealogical Index (IGI) at
www.familysearch.org lists the following children of this couple, who were married at rathven on 12 July 1845:
Margaretta, baptised 4 December 1845, Rathven
Jane, baptised 4 September 1847, Rathven
Martha, baptised 18 December 1849, Edinkillie
Robert, baptised 12 March 1852, Edinkillie
Anne, baptised 11 April 1854, Edinkillie
George, born 21 May 1856, Edinkillie
Eliza, born 30 October 1860, Edinkillie
Annabella Grant, born 18 May 1863, Edinkillie
Charles Mitchell, born 15 July 1864, Edinkillie
Emily, born 20 October 1866, Edinkillie
Williamina Thomson, born 7 December 1868, Elgin
So you can see that they must have moved from Rathven to Edinkillie between 1847 and 1849, and from Edinkillie to Elgin between 1866 and 1868. So they ought to be in Edinkillie in both 1851 and 1861.
You can look up the 1861 census online at
www.scotlandspeople.gov.ukThe 1851 isn't online yet, but the Aberdeen and North-East Scotland Family History Society
http://www.anesfhs.org.uk/ has produced an index which is available to members and on CD-ROM.
HTH