Inside a white envelope with a candy cane border, there was a picture of a young boy with a blue and yellow scarf and a toothy grin.

It was one of Lynne McKenzie's favourite pictures of her son, Jack, the boy who was "always smiling and laughing" and playing with his favourite spiky ball.

The envelope sat atop a basket filled with silver parcels, and Lynne was scanning a small cafe near her home in Elgin for a smile to give it to.

She spied a lady, sipping coffee and laughing with a group of friends, and walked over to her table with the basket in hand.

Lynne only had a few seconds to explain to the pleasant looking woman that her son had passed away last year, and that she and her daughter were coping by making strangers smile.

"We can't buy our darling boy Christmas gifts this year," she said. "We want to keep his memory alive by passing his smile on, and giving some gifts to strangers."

The lady took it, cried, kissed Lynne on the cheek and the brave mother moved on. What started off as one or two parcels soon turned into a mission for a grieving mother to spread her son's smile.

Since then, Lynne and her daughter Holly have spent the last two months delivering 18 random acts of kindness to strangers, each one celebrating a year that Jack was in their lives.

Jack was only 10 months old when he was first diagnosed with Cerebral Palsy, and he and his family were suddenly faced with difficult years ahead.

He took his first wobbly steps when he was two years old after spending most of his early years working through countless physiotherapy exercises by laughing on his mother's knee or rolling around on the living room floor.

His feeble legs soon grew stronger, allowing him to walk faster, and he quickly learned to run around and began to climb everything in sight.

But his mobile years were not to last, and Jack found himself confined to a wheelchair just before his fifth birthday.

"Jack couldn't be on his own after that," says single mother Lynne. "He could have between 40 and 100 seizures per day, and he couldn't do anything for himself.

"He couldn't speak or sign, so he had to communicate purely through body language.

"His face was so expressive - he was definitely the champion of shade."

The house began to transform as Jack's condition worsened - furniture was moved around so that he could lie on the floor, and Lynne and her daughter Holly found they had to change their routine to suit his needs.

"He was always the centre of the house," says Holly, and she laughs when she remembers how spoiled he used to be.

"He had a massive wardrobe filled with lovely clothes, so he'd look beautiful in his wheelchair whenever we went out - and then you'd get mum and me trudging behind him in joggers and messy hair.

"For us, it was all about him."

The family trio would spend the time outside of hospital doing everything that Jack loved - they would take day trips to different cities, and even ventured to Paris to meet Mickey Mouse and his gang.

But nothing excited Jack more than his 18th birthday party.

"We stayed up until three in the morning getting everything ready," says his sister.

"We were covered in paint and glue, but we didn't care - we were going to make it his best birthday ever."

Although recovering from a recent hip replacement, 22-year-old Holly focused all her efforts into making Jack a surprise costume for his superhero-themed party - a cardboard Batmobile to fit around his wheelchair.

"He absolutely loved it," says Lynne. "Everybody got their picture taken with him in the photo-booth - it was just amazing."

Jack passed away just weeks after his birthday, and suddenly Lynne and her daughter were plunged into extreme financial difficulty.

"We were really struggling with money, so we had to do something that most people can't even bear to think of - we had to start selling a lot of Jack's things," says Lynne.

"It was horrible having to do it, but it was either that or we would lose our home."

His mobility equipment was first to go, then some toys that he had unwrapped on his 18th birthday and did not get a chance to play with.

Soon, most of Jack's precious possessions were gone, and Lynne felt as though the last pieces of her son were going with them.

"We were absolutely miserable," says Lynne, with a slight crack in her voice.

"We were being forced to sell all our things just to keep us going, but we wanted to do something that made us happy."

December was only a few hours away when Lynne realised she wouldn't be able to buy Jack presents for Christmas, and it was then that inspiration struck.

"Some of the things we were selling were brand new," she says. "Even though we needed the money, I thought that it might be nice to give some of it away.

"We had the power to make someone else smile - it would be silly not to try."

And so the pair began wrapping some of Jack's things, adding in chocolates and a little letter explaining their mission to their unknown recipients.

"It started off as just one or two gifts," says Lynne. "But then we decided to do 18 random acts of kindness, to represent each year of Jack's life.

"In return, we wanted them to pay it forward, either with their own act of kindness or a small donation to charity."

The first recipient was Linda, a lady in a cafe who kissed their cheeks when they told Jack's story and their mission to keep his memory alive through kindness.

Next was George, a happy council worker who was helping teach some cyclists how to inflate tyres in the park.

"Jack loved being on his bike," says Holly.

Others included Lucy, a brave six-year-old girl raising money for the Royal Aberdeen Children's Hospital where Jack had spent many months.

The list went on, and soon the mother and daughter team were down to their last act of kindness in Jack's name.

"We were quite weepy about our last gift," says Lynne. "We decided to give all of Jack's remaining toys to a playgroup that Jack used to attend.

"We would much rather somebody carried on Jack's memory by playing with the toys, instead of them just lying in our cupboard."

On Wednesday, Lynne and Holly went hand-in-hand into the playgroup Jack had loved and handed over all his toys.

It was a tough, emotional, but ultimately positive final moment that Lynne says was a perfect ending to their challenge.

"I think the best thing for us is that we're keeping Jack's memory alive," says Lynne. "He was a very awesome human being.

"I miss his gorgeous smile - the world is a far far duller place without him."

"I made a promise to Jack," adds Holly. "I promised that I wouldn't let him be forgotten, and that I would make him live forever.

"He was my hero."

To keep up to date with Lynne and Holly's journey in kindness, follow their Facebook page.