From the information you already possess, it was thought that Colin Stewart Beveridge was born in December 1941. There is a computerised index to births, deaths and marriages, in Scotland, after 1855. These records can be viewed on microfiche. There was no reference to Colin's birth in 1941, but there was in the following year:

On 10 December 1942, 6h 30m AM, at Rosehill, Inverkeillor
COLIN STEWART BEVERIDGE was born; son of Donald Stewart Beveridge (Farm Servant) and Frances Wright Beveridge maiden surname Grieve
Date of parents' marriage: 8 August 1931, Hillhead, Premnay
Informant: Donald S. Beveridge, Father, Present
Registered on 14 December 1942 at Inverkeillor Registrar: David Walker, Interim
Registrar
[Inverkeillor 293/1942/31]

In the index to births, the maiden name of the mother (if known) is mentioned alongside each entry. I searched each year from 1931 to 1942, first for male births, named Beveridge, mother's maiden name Grieve, and then female births. I found several possibilities. Each of the births took place in a different parish, but that was quite usual for a farm servant, who moved from farm to farm with the work. I looked at the most recent birth first, that of Rena Evelyn Beveridge in 1939:

On 6 August 1939, 1h 30m PM, at Dalladies, Fettercairn
RENA EVELYN BEVERIDGE was born; daughter of Donald Stewart Beveridge (Farm Servant) and Francis Wright Beveridge maiden surname Grieve
Date of parents' marriage: 8 August 1931 at Hillhead of Premnay, Insch
Informant: Donald S. Beveridge, Father, Present
Registered on 21 August 1939 at Fettercairn
Registrar: Agnes Preston
[Fettercairn 257/1939/8]

I then searched the index to deaths, from 1939 to the present day, for a reference to the death of Rena Evelyn, but did not find one. She has not died in Scotland. However, neither has she married in Scotland either.

There was a reference to the birth of Valerie Keillor Beveridge in 1937. When I looked at this birth certificate on microfiche, it proved to be the wrong family. Another possibility was the birth of Catherine Francis in 1932:

On 6 October 1932, 0h 30m AM, at Lower Craighill, St. Cyrus CATHERINE FRANCIS BEVERIDGE was born; daughter of Donald Stewart Beveridge (Farm Servant) and Francis Wright Beveridge ms Grieve
Date of parents' marriage: 8 August 1931, Hillhead, Premnay
Informant: Donald Beveridge, Father, Present
Registered on 8 October 1932 at St. Cyrus Registrar: Herbert Hay
[St. Cyrus 267/1932/14]

According to the index to deaths, from 1932, Catherine Francis has not died in Scotland to the present day either. However, she did marry, in 1953:

On 8 August 1953 at St. Columba's Manse, Park Road, Brechin, After Banns According to the Forms of the Church of Scotland
NORMAN CURRIE, Plumber, journeyman (Bachelor) age 23 years, of 9 Airlie Street, Brechin; son of Charles Currie (Distillery Worker) and Jessie Currie ms Henderson
Marriage to
CATHERINE FRANCES BEVERIDGE, Assistant Hotel Cook (Spinster) age 20 years, of Reedie Cottages, by Kirriemuir; daughter of Donald Stewart Beveridge (Farm Grieve) and Frances Wright Beveridge ms Grieve (deceased)
Minister: Geo. F. Brown, Minister Pro tem, Maison Dieu Church, Brechin
Witnesses: George Mong, East Pittendriech, Brechin, Agnes Mugg, Reedie Cottages, Kirriemuir
Registered on 10 August 1953 at Brechin
Registrar: S.A. Stamford
[Brechin 275/1953/56]

According to this certificate, Frances had died. I began by looking at the index to deaths for 1953, and found a reference immediately:

On 14 May 1953, 1h 50m AM, at Fyfe Jamieson Maternity Home, Forfar (usual residence, Reedie Cottages, by Kirriemuir)
FRANCES WRIGHT BEVERIDGE (Married to Donald Stewart Beveridge, Farm Grieve) died age 40 years; daughter of James Grieve (Crofter, deceased) and Jane Ann Grieve (afterwards McPherson) ms Mackie
Cause of death: Pulmonary Embolism. Confinement in Progress - before actual birth, as certified by James C. Walker, MBChB
Informant: Donald Beveridge, Widower, Reedie Cottages, by Kirriemuir
Registered on 14 May 1953 at Forfar
Registrar: Wm. Rodger
[Forfar 288A/1953/56]

I then looked again at the index to births for 1953, but could not see the birth of a male or female Beveridge, mother's maiden surname Wright. Nor was there a reference in the death index. I think the child may have been stillborn, and therefore not registered.

Searching through the index to male deaths, from 1953, I saw a reference to the death of Donald Stuart Beveridge in Forfar in 1996:

On 30 March 1996, 1940 hours, at Infirmary, Arbroath Road, Forfar, DD5 2HS (usual residence - )
DONALD STUART BEVERIDGE, Lorry Driver (retired), born 28.5.1909, age 86 years, Widowed 1st Frances Wright Grieve, Domestic Servant, 2nd Marjory Donaldson, Shop Manageress; son of John Beveridge (Crofter, deceased) and Elizabeth Lawrie or Beveridge (deceased)
Cause of death: I(a) Carcinomatosis II Dementia, as certified by G.S.D. Peterkin
Informant: A. Beveridge, Son, 13 Grampian Drive, North Muir, Kirriemuir, DD8 6TN
Registered on 1 September 1996
Registrar: Wilma M. Burnett
[Forfar 364/1996/83]

Fortunately, Donald lived to a great age, making his death a comparatively recent event. Searching through the index to births after 1942, I found a reference to the birth of Alexander Beveridge:

On 16 May 1946, 2h 10m AM, Fyfe Jamieson Maternity Home, Forfar
ALEXANDER JOHN BEVERIDGE was born; son of Donald Stewart Beveridge (Farm Servant, usual residence Sandyford, Parish of Kirriemuir) and Frances Wright Beveridge ms Grieve
Date of parents' marriage: 8 August 1931 at Insch, Aberdeenshire
Informant: Donald S. Beveridge, Father
Registered on 28 May 1946 at Forfar
Registrar: Wm. Rodger, Assistant
[Forfar 288A/1946/198]

I could not see references to any other births, between 1942 and 1953, either male or female.