He and Harriet had 4 s. and 6 daus.

From the 1851 census all the children survived to 1861

The 1861 census in fact shows 3 s. and 7 daus (plus 24 or so servants - where did they put them all!) at Drayton House, Drayton Road, Lowick, Thrapston, Northamptonshire:

First name(s) Last name Relationship Marital status  Gender  Age  Birth year  Occupation  Birth place
William B     Stopford Head  M  M  55  1806  Magistrate Landed Proprietor  Barton Seagrave, Northants
Caroline H    Stopford Wife  M  F  45  1816  -                             Lowick, Northamptonshire
Harriet C     Stopford Daur  U  F  22  1839  -                             London, Middlesex
Fanny L       Stopford Daur  U  F  18  1843  -                             London, Middlesex
Georgiana M   Stopford Daur  U  F  18  1843  -                             London, Middlesex
Lionel R      Stopford Son   -  M  16  1845  Scholar                       London, Middlesex
Alexander Wm  Stopford Son   -  M  14  1847  Scholar                       London, Middlesex
Margaret E    Stopford Daur  -  F  13  1848  Scholar                       London, Middlesex
Sydney R      Stopford Son   -  M  11  1850  Scholar                       London, Middlesex
Mary E        Stopford Daur  -  F   9  1852  Scholar                       London, Middlesex
Beatrice E    Stopford Daur  -  F   7  1854  Scholar                       London, Middlesex
Grace         Stopford Daur  -  F   6  1855  Scholar                       London, Middlesex

Address & Ref:
Archive reference  RG09
Piece number       959
Folio              93
Page number        10
Combine:           1861 ref: RG09, piece 959, folio 93, p. 10
________________

The Royal Licence in The Gazette:

London Gazette dated April 5 1870:

                                 “Whitehall March 26, 1870

  “The Queen has been pleased to grant unto William Bruce Stopford, of Drayton House, in the parish of Lowick, in the county of Northampton, Esq., in the Commission of the Peace and a Deputy Lieutenant for that county, and to Caroline Harriet Stopford, his wife (formerly Caroline Harriet Stockville), the only child and heir of George Germain, Esquire, commonly called the Honourable George Germain, and grand-daughter of George Germain (formerly George Sackville), Viscount Sackville, of Drayton, both deceased, Her Royal Licence and authority that they may take the surname of Sackville, in addition to and after that of Stopford, and that he the said William Bruce Stopford may bear the arms of Sackville quarterly with those of Stopford, and that such surname and arms may in like manner be taken, borne and used by the issue of their marriage; such arms being first duly exemplified according to the laws of arms and recorded in the College of Arms, otherwise the said Royal Licence and permission to be void and of none effect.
  “And to command that the said Royal concession and declaration be registered in Her Majesty’s said College of Arms.”
________________

In 1871 only the daughters were at home at Drayton House, Lowick, Thrapston, Northamptonshire:

W B Stocpford  Sackville  Head  M  M  65  1806  Magistrate Landowner  Northants, Barton Seagrave
Caroline H     Sackville  Wife  M  F  55  1816  -                     Northants, Drayton House
Harriet C      Sackville  Daur  U  F  32  1839  -                     London, St George’s Hanover Sq
Fanny L        Sackville  Daur  U  F  29  1843  -                     London, St George’s Hanover Sq
Margaret E     Sackville  Daur  U  F  23  1848  -                     London, St George’s Hanover Sq
Elizabeth Mary Sackville  Daur  U  F  19  1852  -                     London, St George’s Hanover Sq
Beatrice E     Sackville  Daur  U  F  17  1854  -                     London, St George’s Hanover Sq
Grace          Sackville  Daur  U  F  16  1855  -                     London, St George’s Hanover Sq
  plus 9 plus 17 totals 26 live-in servants

Ref:
Archive reference  RG10
Piece number       1507
Folio              99
Page               15
Combined:          1871 ref: RG10, piece 1507, folio 99, p. 15
________________

Let’s see if I can put together all the children also from the registrations, not to mention baptisms:

Registrations: Search for all Stopfords with a mother’s maiden name of Sackville and born between 1837 and 1857:

Name: Mother's Maiden Surname:
STOPFORD, HARRIET  CAROLINE   SACKVILLE  
GRO Reference: 1838  D Quarter in SAINT GEORGE HANOVER SQUARE  Volume 01  Page 15
STOPFORD, FRANCES  LOUISA   SACKVILLE  
GRO Reference: 1841  D Quarter in SAINT GEORGE HANOVER SQUARE  Volume 01  Page 8
STOPFORD, GEORGINA  MARY   SACKVILLE  
GRO Reference: 1842  D Quarter in SAINT GEORGE HANOVER SQUARE  Volume 01  Page 10
STOPFORD, LIONEL  RICHARD   SACKVILLE  
GRO Reference: 1845  M Quarter in ST. LUKE CHELSEA  Volume 03  Page 39
STOPFORD, ALEXANDER  WILLIAM   SACKVILLE  
GRO Reference: 1846  S Quarter in SAINT GEORGE HANOVER SQUARE  Volume 01  Page 27
STOPFORD, MARGARET  ELIZABETH   SACKVILLE  
GRO Reference: 1847  D Quarter in SAINT GEORGE HANOVER SQUARE  Volume 01  Page 14
STOPFORD, -     SACKVILLE    ( male )
GRO Reference: 1850  M Quarter in SAINT GEORGE HANOVER SQUARE  Volume 01  Page 23

The boy born in 1850 was probably Sydney Robert and the last to be registered.  I cannot find registrations for Mary in 1852, Beatrice in 1854 or Grace in 1855.  Who was baptized and published?

Baptisms: Search for Stopford surnames with parents of William and Caroline:

No baptisms on FindMyPast.  Several on Ancestry:

1838 Dec 6th   Harriet Caroline    St Peter Pimlico    Wm Jamie & Caroline Harriet   Scan
1840 Apr 28th  Sackville George    Ecton, Northants    Wm Bruce & Caroline Harriet   No
1841 Dec 10th  Fanny Louisa        St Peter, Pimlico   Wm Bruce & Caroline Harriet   Scan
1842 Dec 18th  Georgina Mary       St Peter’s Pimlico  Wm Bruce & Caroline Harriet   Scan - twice!
1845 Feb 19th  Lionel Richard      St James, Westm’r   Wm Bruce & Caroline Harriet   No
1846 Sep 27th  Alexander William   St Paul, Wilton     Wm Brice & Caroline Harriet   Scan
1847 Nov 7th   Margaret Elizabeth  St Paul Wilton      Wm Bruce & Harriet Caroline   Scan
1850 Apr 7th   Sydney Robert       St Paul, Wilton Place  Wm Br & Caroline Harriet   Scan
1851 Jun 25th  Eleanor Mary Agnes  St Paul’s Knightsbridge  Wm B & Caroline Harriet  Scan - Extra
1853 Aug 9th   Beatrice Evelyn     St Paul’s Knightsbridge  Wm B & Caroline Harriet  Scan
1854 Oct 1st   Grace               St Paul’s Knightsbridge  Wm B & Caroline Harriet  Scan

This has found, in addition, Beatrice and Grace and one not in the censuses, Eleanor Mary Agnes, though she was indexed as Stoppard.  But still NOT Mary.  And we are short of a name for Sydney.

But finding that Eleanor was omitted as Stopford has been indexed as Stoppard led to finding that Sydney was the same.  And later to finding that Harriet Caroline had been indexed as Stafford.

A final search was made on Ancestry for all their children in one go.  This had these criteria:

Forename:   [blank]
Surname:    St*
Birth:      1848 ± 10 years
Place:      England (broad)
Father:     William (only)
Mother:     Caroline Harriet (only)

This brought up 12 baptisms including the first son of Sackville George, born in 1840 in Northants; it also had the two separate baptisms for Georgiana.  But still no sign of Mary Elizabeth, as such in the 1861 census and as Elizabeth Mary in the 1871 census; she may have died soon after that.

7 births on the GRO.  12 baptisms on Ancestry, one twice.  1 child no baptism found.
________________

His death index:

First name(s)  WILLIAM B S
Last name      SACKVILLE
Gender         Male
Birth year     1806
Age            66
Death quarter  2
Death year     1872
District       St. George Hanover Square
County         London
Volume         1A
Page           214
Country        England
Record set     England & Wales Deaths 1837-2007
_______________

His burial transcription:

First name(s)       WILLIAM BRUCE
Last name           STOPFORD-SACKVILLE
Birth year          1806
Death year          1872
Age                 66
Burial year         1872
Burial day          01
Burial month        Jun
Residence           Lowick Drayton House
Parish              LOWICK
County              Northamptonshire
Country             England
Register reference  B0262/0440
Record set          Northamptonshire Burials
_____________

His probate index:

Effects under £18,000.

24 August.  The Will of William Bruce Stopford-Sackville formerly William Bruce Stopford late of Drayton
House in the County of Northampton Ewsuire who died 29 May 1972 at 7 Grosvenor-gardens in the County of Middlesex was proved at the Principal Registry by Caroline Harriet Stopford-Sackville of Drayton House, Widow
the Relict the sole Executrix.
________________

Marriage Licence:

First name(s) WILLIAM BRUCE
Last name STOPFORD
Licence year 1837
Licence date 12 Jun 1837
New calender date 12 Jun 1837
Bride's first name(s) Caroline Harriet
Bride's last name SACKVILLE
Groom's first name(s) William Bruce
Groom's last name STOPFORD
Place Dioceses of England & Wales
Record set Faculty Office Marriage Licences
__________________

Marriage transcription:

First name(s) WILLIAM BRUCE
Last name STOPFORD
Title Esq
Marriage year 1837
Marriage day 20
Marriage month Jun
Marriage place LOWICK
Parish Westminster St Margaret Mdx
Marital status B
Spouse's first name(s) Caroline Harriet
Spouse's last name Sackville
Spouse's title -
Spouse's parish Lowick
Spouse's marital status S
Event Type Marriage
By Banns or licence License
County Northamptonshire
Country England
Record set Northamptonshire Marriages
______________