Katherine Parr's role as a step-mother has always been seen as central to her life and her success as Queen. It seems clear from the records and extant correspondence that she had a warm relationship with all of her five step-children, with the possible exception of Lord Latimer's son, John. Novels occasionally assert that she had step-children older than herself, but this is presumably based on the now discredited theory that her first husband was Sir Edward Burgh the elder, rather than his grandson of the same name.

Katherine's first experience of a maternal role would have been in 1534 when she travelled to Snape Castle as the wife of John Neville, 3rd Baron Latimer. Latimer had two children from his first marriage, John, later 4th Baron, and Margaret Neville. John was around 14 at the time of his father's third marriage and Margaret perhaps five years younger. They had already had a short experience of a step-mother, but Latimer's second wife died within two years of marriage, leaving no children of her own.

In an era when the vast majority of people were married at least twice, their father's remarriage cannot have surprised the Neville children. Katherine Parr, as a member of an important gentry family in the north, and a kinswoman, was an unexceptionable choice, and it appears that she took an immediate and active interest in the education of Margaret, winning a love and respect from the young girl that would last all of Margaret's short life.

It seems to have been rather different with John. His subsequent history suggests that he was a violent man, and Katherine later wrote

Younglings…are offended at small trifles, taking everything in evil part, grudging and murmuring against their neighbour..

which strongly suggests experience of a sulky teenager.

Nevertheless, whatever the difficulties of his adolescence, young John's wife, Lucy Somerset, was later appointed as one of Katherine's ladies-in-waiting.

The most terrifying incident in the lives of Katherine, Margaret and young John would have been the attack on Snape by the rebels in 1537.

The three of them were alone and unprotected by Lord Latimer who had been commanded to London to explain himself to the King and Council and beg for pardon for his part in the Pilgrimage. Latimer wrote to his friend Norfolk, lamenting his inability to protect his family as he was ordered to Doncaster. In the event, he ignored his immediate orders and raced towards Snape to effect a rescue. By the time of his arrival, however, the rebels had left. Latimer left again, to head for Pontefract, leaving Katherine and the children behind.

John Neville, 4th Baron Latimer, Katherine Parr's step-son, at rest in Well Church, Yorkshire.

As was common at the time, Margaret had been betrothed young, to Ralph Bigod, a son of Sir Francis Bigod. Unfortunately, Sir Francis, although a reformer, was one of the ring leaders of a second wave of revolt after which it was unthinkable that Latimer, who was desperately trying to shore up relations with the King, would let the match go forward. We cannot know what Margaret's reactions were - she may have been sorry that her match to a man she knew had been broken off, perhaps to be replaced by a wedding to a complete stranger. Whatever her feelings, we can safely assume that Katherine was her support.

During the first years of queenship, Katherine was attended by Margaret Neville, but sadly the girl died in 1545, probably aged no more than twenty. In her will, she speaks her regard of Katherine, and the will itself, which strongly reflect the reformed religion, suggests that Katherine had influenced her religious views markedly.