The marriage records of the children of John and Mary Ann Aiken may have Mary Ann cited by her maiden name. Further, grandparents were often godparents to the first/earliest born. I suggest you mine the parish records for as many documents/records as you can find on the line. The purpose of this exercise is to build confirmation of a name, before pursuing a guess.
Where to find the parish records? Check the familysearch.org library catalog, search the area they resided in, and see what's available. Films can be ordered on-line and sent to your local FHC for viewing. The instructions of how to do this are on the familysearch.org site.