The 1841 Census shows Alexander as 1 month old living at Damhill Smithy (wrongly transcribed as Camhill) with parents Alexr and Elizabeth and siblings Samuel 15, Robert 11, Agnes 8, Marion 7, Elizabeth 5 and Janet 2. Parents' ages given as 35 but in 1841 Census ages of adults were "rounded down" to nearest 5 years so not necessarily accurate!
IGI shows 2 marriage entries for Alexander Thomson and Elisabeth Wiseman - 13 Mar 1824 in Avondale parish (Strathaven area) and About 14 Mar 1824 in Douglas parish. This suggests one partner came from each parish, so the marriage was entered in both registers.
There are a number of children born to this couple - a mixture of extracted baptism dates (from Old Parish Registers) and submitted birth dates (by members of LDS):-
Samuel - born 19 Feb 1825, Douglas
Lilias - baptized 15 April 1827, Douglas
Agnes - baptized 28 Oct 1832, Lesmahagow
Marion - baptized 21 Sept 1834, Lesmahagow
Elizabeth - baptized 14 Aug 1836, Lesmahagow
Janet - baptized 19 May 1839, Lesmahagow
Alexander - born 02 May 1841, Lesmahagow
The 1841 Census was carried out on 07 June, so that would fit in with Alexander being one month old.
I live just a few miles from Damhill (I know the farms surrounding it, but had never heard of Damhill). When I get a chance I will drive over and see what's there.
Lizci