Erin Westmeijer, who suffers from leukaemia, with her mother Christina, father Jeroen and sister Caitlyn / JOHN LAWRENCE

Matilda Battersby discovers how the incredible support of the Rainbow Trust helped a family cope with a devastating illness

The Westmeijer family home in Surrey is unbelievably Christmassy. A tree covered in lights dominates the lounge, stockings hang on the fireplace and there are decorations everywhere. The youngest Westmeijers, Caitlyn, five, and Erin, two-and-a-half, charge around happily, repeatedly pressing the soft tummies of stuffed toys that play music, filling the house with conflicting Christmas tunes and laughing excitedly.

"That's enough now," says Christina, their mother, hiding her smiles behind a large cup of tea as we wait for the chaos to subside. The contrast between this and last year's Christmas is stark. In 2010 little Erin had been in and out of hospital undergoing gruelling treatment for acute lymphoblastic leukaemia, and it was uncertain right up until Christmas Eve, whether she would be allowed home. After just two days of festivities, Erin had a reaction to her treatment and was back in hospital until the new year.

Watching Caitlyn and Erin playing together a year on, they appear to be very healthy, happy girls. But it has been a difficult time for both of them. After 15 months of aggressive chemotherapy, Erin is now on a lower dose and recovering her strength. After coping with Erin's treatment in hospital, during which time at least one of her parents needed to be by her bedside at all times, Caitlyn has had to put aside the normal demands of a growing five-year-old and get used to not seeing her parents together, and being cared for by relatives and friends.

"I relied heavily on friends to pick Caitlyn up from school," Christina says. "When my husband, Jeroen, finished work he would come straight to the hospital and then I'd go and collect Caitlyn. In the beginning, when she was first diagnosed, I stayed with Erin all the time. But once she was moved to the Royal Marsden, an hour's drive away, Jeroen and I took turns to stay overnight with her. This was partly because you don't get much sleep on a night shift, and partly because I realised Caitlyn needed to see us both."

Nearly eight months after Erin was diagnosed, the Westmeijers were referred to Rainbow Trust – one of three charities for which we are asking donations for the 2011 Independent Christmas Appeal. The charity allocates a support worker to families who have a child with a life-threatening or terminal condition. These support workers are almost entirely funded through public generosity. They provide emotional and practical care, tailored to the needs of each family.

One of the most neglected of those needs can be the care of the brothers or sisters of the sick child. Siblings can feel isolated, ignored by their parents and unable to understand what is going on. Some 78 per cent of the families Rainbow Trust support juggle the demands of looking after sick and healthy siblings.

In the Westmeijers' case, Rainbow family support worker Lyn Sweet's task was to ensure Caitlyn's needs were supported so her parents could continue to support Erin. Lyn became somebody Christina or Jeroen could call on at any point and ask anything of, without feeling it was too much to request. Lyn has driven to and from the Royal Marsden to help out with appointments, been on call to collect Caitlyn from the family's local hospital in Frimley, Surrey, and has picked Caitlyn up from school, taken her on days out during the summer holidays and entertained both children and parents with craft sessions.

"When I first met the family, I think it would be fair to say that they were very good jugglers," Lyn says. "It was very difficult to know where they were going to be week on week and that could affect Caitlyn. She is a busy little girl and hospitals are not the greatest places to play and have fun in. I would come in and give her some time to be Caitlyn."

Jeroen and Christina have clearly provided fantastic care for Caitlyn in an impossible situation, but are aware that there have been moments when, like any child, she has felt the strangeness of it. Hospitals are quite isolating for healthy children and, particularly during the school holidays, Caitlyn would find herself without any kind of normal routine, unable to attend swimming lessons or visit her friends.

"Caitlyn was an absolute star. She never moaned that she wasn't getting enough attention," Christina says. "But it did affect her behaviour at some points," Jeroen adds. "All she needed was a little quality time and I can't stress enough how helpful it has been having Rainbow."

The family has been very open with Caitlyn about her sister's condition and what it means. So much so that Caitlyn is now something of a biology expert. After a recent fall at school, she bravely piped up to the nurse patching up her knee: "Oh, I'll be all right because I've got platelets to make me better. My sister doesn't have any of those."

Hopefully as Erin improves the Westmeijers will need to call on Lyn less and less. Until then, she'll be there, for Caitlyn or any of them, any time.

Appeal partners: Who we're supporting

Save the Children

Save the Children works in 120 countries, including the UK. They save children's lives, fight for their rights and help them fulfil their potential. Save the Children's vital work reaches more than 8 million children each year - keeping them alive, getting them into school and protecting them from harm.

The Children's Society

The Children's Society provides vital support to vulnerable children and young people in England, including those who have run away from home. Many have experienced neglect, isolation or abuse, and all they want is a safe and happy home. Their project staff provide essential support to desperate children who have no-one else to turn to.

Rainbow Trust Children's Charity

Rainbow Trust Children's Charity provides emotional and practical support for families who have a child with a life threatening or terminal illness. For families living with a child who is going to die, Rainbow Trust is the support they wished they never had to turn to, but struggle to cope without.

At The Independent we believe that these organisations can make a big difference to changing many children's lives.