Many thanks Monica for all your help and advice, I would have replied before now but you have kept be busy
I did check the 1841 Census on Scotlands People and they were all together, I thought it was strange to have a household with just 2 young children. The original image wasn't available on Ancestry.
I now have the following births which you suggested and I believe they are all the same family.
30 Jun 1805 Strathblane, Stirling, Duncan McGrigor
Duncan, son lawful to Grigor McGrigor and Mary Stewart his spouse in town = head Ballioron was baptised.
8 Oct 1809 Strathblane, Stirling, Alexander McGrigor
Alexander, son lawful to Grigor McGrigor, Labourer in Wester?? Blairquhorh and Mary Stewart his spouse was baptised.
14 Mar 1813 Strathblane, Stirling, Mary McGregor
Mary, lawful daughter of Gregor McGrigor in G???sicle and Mary Stewart his spouse was baptised 14 Mar 1813.
4 Dec 1803 Strathblane, Stirling, Catharine McGrigor (my 4 x g grandmother)
Catharine, lawful daughter to Grigor McGrigor and Mary Stewart in (too faint to read) was baptised.
I can't find the marriage of Gregor McGregor and Mary Stewart and have tried many variations of the spellings and it doesn't appear to be there. Because they both died prior to 1855 I don't think there's much chance of finding more on them. A search for a birth for Gregor McGregor brought up too many possibilities.
There was a Duncan McGregor who marr Jean Stewart 1 Nov 1801 Fortingall, Perth and I was wondering if he could have been a brother of Gregor (and/or poss sister of Mary Stewart), maybe I am clutching at straws there.
Thanks again for your help, it is very much appreciated.
Rachel