......On Scotlands People, it appears that Sarah Pool Alston died in 1954 at Moffat, aged 77. Also, a person named Robert Todd (probably her husband) died at Moffat, aged 72 in 1959.
So it looks like the Todds settled in Moffat and died there.
I searched for children named Todd, who were connected with Moffat after the date of Robert & Sarah's marriage in 1910. There was a George Alston Todd who died in 1989 at Moffat, aged 78, so he would be born about 1911, and as Sarah Alston & Robert Todd were married in 1910, this looks like their son.