Thanks for all your ideas.
The photos are in a little red album that was owned by my grandmother Dorothy, who lived from 1894 until the 1980s.
Her husband William lived from 1885 to 1938. It's definitely not them and their children.
So, I've been thinking that it's either Dorothy's siblings and mother, or William's siblings and mother.
Here are William's brothers and sisters, and dates of birth (and death if I know them) - they all grew up and got married:
George Albert H. Keeling (1880)
Archibald Albert Keeling (1881)
Emily Kate Keeling (1884 - 1957)
William Ernest Keeling (1885 - 1938)
Elsie Alice Keeling (1887)
Douglas Harry Keeling (1889 - 1931)
Leslie Alfred Stanley Keeling (1891)
And mother and father:
Emily Bolt (1852)
George John James Keeling (1853 - 1902)
That doesn't seem to fit to me.
So, for Dorothy:
Millicent Jane Purchase (c1879)
Richard William Roberts-Purchase (1880 - 1930)
(Lily) Lilian Mary Purchase (1881)
(Bertie) Herbert Allen Purchase (1882)
Reginald Roberts Purchase (1886)
Edith Annie C. R. Purchase (1889)
Percival Edgar Purchase (1893)
Dorothy Ellen Roberts-Purchase (1894)
And parents:
Mary Selina Jones (1860)
Richard Roberts Purchase (1855)
And that also doesn't seem to quite fit to me, either.
My best guess is that Percival Purchase is the boy, and the ladies are some combination of Dorothy, Edith, Lilian and the mother Mary.
The father was a jeweller / watch maker, so perhaps he gave the boy that flash watch chain!
What I really need is for somebody to have written the names on the back of one of the pictures!