The Duchess of Cambridge celebrates her 35th birthday on Monday.

Kate is expected to mark the occasion privately with the Duke of Cambridge and her children Prince George and Princess Charlotte, ahead of her first public engagements of the new year.

On Wednesday, the Duchess is dropping in on an Early Years Parenting Unit at the Anna Freud National Centre for Children and Families in north London to learn more about their work with families with children under five years old.

The unit offers an assessment and treatment programme for groups of parents with personality disorders, and their children, who are at risk of being taken into care.

Kate will also carry out a joint engagement with William the same day when they visit a Child Bereavement UK Centre in Stratford, east London, to mark its first anniversary.

Royal watchers are waiting to see whether 2017 will be the year the Cambridges expand their brood.

Kate, who is one of three herself, is thought to be keen to have another child – a sibling for George and Charlotte.

George, who turns four in July, is due to start school in September. Although no official announcement has been made, he is expected to attend the same one as his father William – the Wetherby Pre-Preparatory School in west London.

It would mean a move back to Kensington Palace for the Cambridges from their country retreat, Anmer Hall in Norfolk.

The Duchess has her sister Pippa’s wedding to look forward to in May.

Pippa is marrying financier boyfriend James Matthews near the Middleton family home in Bucklebury, and George and Charlotte are expected to act as page boy and flower girl.

Kate will also be supporting her husband as he prepares to mark the 20th anniversary of the death of his mother Diana, Princess of Wales in August.

Prince George and his mum last year.

The past year saw the Duke and Duchess travel to Bhutan and India, celebrate Charlotte’s 1st birthday, George’s 3rd birthday, and take their family on a busy tour of Canada.

The Duchess, who has now been a member of the Royal Family for nearly six years, was born Catherine Elizabeth Middleton at the Royal Berkshire Hospital, Reading, on January 9, 1982.

She met William while studying at St Andrews University in Scotland, and after a long courtship married her former flatmate at Westminster Abbey on April 29, 2011.

-AAP