Julia Margaret Cameron National Portrait Gallery February 6 to May 26

Long before Chitty Chitty Bang Bang came up with its famous child-catcher, a similarly relentless kiddy-collector was at work on the western end of the Isle of Wight. Her name was Julia Margaret Cameron, she was an ardent photographer in the 1860s and, of course, her intentions were innocent. But it’s easy to see how a keen camera enthusiast, lurking behind a briar hedge and desperate for sitters, might look to a Victorian child’s imagination like a kind of female Bill Sikes.

“Children loved but fled from her,” wrote Edith Nicholl Ellison, in her 1906 memoir, A Child’s Recollections of Tennyson. “I can see her now, clad in the never-failing wrapper, stained - as were her hands and eager face - with the chemicals she used in her work, her hair falling any way but the right way, lying in wait at her garden gate for the young onesI ‘She’s coming! She’ll catch one of us!’ And sure enough an arm would intercept the passage of some luckless wight, andI the victim was led away.”

No one seems to have wanted to sit for Mrs Cameron. Almost all who did it, during her great photographing years of 1864-75, belly-ached about it afterwards. So one question is inevitably raised by the National Portrait Gallery show devoted to her work: wasn’t it a miracle that she got so many children to pose for her? Sometimes in wings? After all, her exposures would require several minutes of difficult static posing, and she would detain sitters in her studio (a converted chicken-house at the back of her home at Freshwater Bay) for umpteen exposures until she finally secured one that satisfied her.

No wonder “She’ll catch one of us!” was the cry. Judging from their rate of appearance in these pictures, local children such as the young family of Thomas Keown (an officer at the nearby Freshwater Redoubt) seem to have known no other juvenile pastime than sitting close to a camera lens, clutching lilies. Did Mrs Cameron really once lock a child in a cupboard to get the right expression for a picture called “Despair”? I suspect the title suggested itself afterwards. A beautiful blond infant called Freddy Gould crops up with worrying frequency in Mrs Cameron’s pictures. He must have had the most placid disposition or the slowest legs in Freshwater.

Mrs Cameron was a magnificent photographer with an unmistakable style. The NPG’s show, curated by Colin Ford, demonstrates the full range of her achievements, only some of which will be familiar. There are those dreamy, pale, young idealised women - in fact, usually Mrs Cameron’s housemaids - dressed in cheesecloth, yard-long hair swept back, wearing expressions of awe. Perhaps best known are the large portrait heads of Victorian (male) celebrities, in which full attention is paid to prominence of temple and luxuriance of beard. Famously, Mrs Cameron photographed friends such as Alfred Tennyson, Thomas Carlyle and G F Watts, and made them look like biblical kings and prophets, only a bit more exalted.

The gaps in Mrs Cameron’s interests are significant: she had no time for men without big brains, women over 18 or ugly children. Her reverence for beauty (so the theory runs) derived from growing up plain in a family of stunners. While her sisters were nicknamed “Dash” and “Beauty”, Julia Margaret was known as “Talent” - an obvious family consolation prize. But at least she grew up without illusions. When an Isle of Wight neighbour, a Mr Peacock, once hinted to Mrs Cameron that plain people should be eliminated, she replied with spirit, “What would become of you and me, Mr Pocock?”

With all those wise men and fair maidens to keep her busy, though, why did Mrs Cameron keep ambushing children? Well, partly because they were easier to bully than grown-ups (and could plead fewer legitimate previous appointments), but also because, to the mid-Victorians, children were near to God, and couldn’t help trailing clouds of glory. Their natural garb was winged nakedness, and it was the job of any devout artist to capture their transient spirituality.

George Bernard Shaw abhorred Mrs Cameron’s pictures of children; especially the ones with the poultry-shop overtones. “No one would imagine that the artist who produced the marvellous Carlyle would have produced such childish trivialities,” he said.

But in terms of the current exhibition, the child pictures are important, not least because they are among the most beautiful in the show. On the one hand, they highlight the whole question of exploitation - a question raised repeatedly in relation to Lewis Carroll’s contemporaneous child pictures, of course. But on the other, they shove that question aside. Seen in the context of her other work - the whole lot presented at the NPG in glorious original prints - Mrs Cameron’s child pictures show how deeply she strove in her art not just to glorify the individual, but to reveal the human soul. OK, she misfired occasionally. Sometimes modern eyes see only a child fed up, bewildered, or anxious about being locked in that cupboard again.

Perhaps Mrs Cameron misjudged the limits of photography. But her camera could look at a child’s face as intently as it looked at a poet laureate’s.

And that was when she really caught the child.

National Portrait Gallery recorded information: 020 7306 0055; www.npg.org.uk. Lynne Truss’s novel Tennyson’s Gift is available from Bruce Holdsworth Books (email bruce@bruceholdsworthbooks.com). She is also the author of Tennyson and his Circle (NationalPortrait Gallery)