The grandmother-of-six was taking Edie, who was just weeks old, for a walk in her pram when she began to picture the world in a few generations' time.
"I looked down at her in the pram and thought, 'I'm a granny, you're a little girl and you might be a granny one day, but what will the Earth be like when you are pushing your granddaughter?'" she recalls.
"That was the moment that I realised I had to do a hell of a lot more than just take my own bags to a supermarket or my bottles to a recycling bin – that wasn't going to do. I knew we had to do something much more radical.
"I have got to do everything I can to help the environment before I fall off my twig and encourage other people to do things too."
So Tillie, 65, and husband John – a retired forester – put their green efforts into full swing shortly after moving into their North Berwick home in 2006.
Now the couple, who have spent more than 40,000 making their home more environmentally friendly, are one of two Lothian families down to the final five in a UK-wide competition to find Britain's greenest family.
The Bairds, along with the McDermids of West Lothian, are contenders for the Future Friendly Awards' family title, with the winner due to be revealed at a ceremony in London on Thursday. The prize is a 10,000 green home makeover, but if they do win the award, the Bairds will probably be scratching their heads as to what else they can do to their house – they already seem to have everything covered.
The first change they made was to introduce a sun room – which absorbs heat during the day – at the front of their three-bedroom house. Next came double-glazing, cavity wall, loft and underfloor insulation, and a new central heating system with an efficient condensing boiler.
Retired community development worker Tillie and husband John, 65, have also filled their back garden with fruit and vegetables, including purple sprouting broccoli, perpetual spinach, strawberries and loganberries, while their front garden features a range of plants that don't need to be watered, and even palm trees.
Tillie laughs: "The back garden is crammed full of food apart from one or two seats sitting in the sun."
The most dramatic and "exciting" change to the couple's home came in February this year when they installed photovoltaic panels on the roof, which convert sunlight into electricity to run household appliances and lighting, at a cost of almost 12,000.
Tillie explains: "We are generating our own electricity and what we don't use gets fed back into the grid, so if we are not using it other people can – it's a renewable energy. You are reckoned to get back 1,000 a year from what you generate and what you save by using your own electricity."
As for the second Lothian couple in the final five, Judith, 42, and George McDermid, 43, a consultant psychiatrist at Wishaw General Hospital, say they are "absolutely delighted" to be in line for the title
Since moving into their five-bedroom bungalow in Burngrange in West Calder in June 1995, the couple – who have two children, Beth, 10, and Rory, seven – have insulated their loft, helping to reduce gas bills to just one sixth of the original cost, as well as installing a new boiler and cavity wall insulation, double glazing and new doors.
Last year, they introduced a wood burning stove to the living room to help lighten their impact on the environment, fuelling it mainly with wood from trees in their back garden.
The couple, who now believe they have saved more money than they have spent on the extensive improvements to their home, occasionally boil pasta on the stove, or heat water for the kids' hot water bottles in the winter.
Judith says: "It's always a case of looking at new things to try and reduce our impact or improve our efficiency. We take little steps and see how we go and if it works it works, and if it doesn't we just try something else.
"When the kids came along, growing our own food became a big thrust of what we were doing. We took a greater interest in the food we eat and where it comes from. We garden organically and compost everything we possibly can.
"From the point of view of looking at climate and the kids' future, we want to leave the planet in as good a condition as we can, and also we want our children to know where our food has come from and that it's not just from a polystyrene tray in a supermarket."
The family's garden, which now has nine raised beds, features apple trees, blackberry and gooseberry bushes, and plenty of vegetables, ranging from onions and potatoes to kale and celeriac.
Beth even suggested that the family should live off food grown in the garden for a period of two months, which they managed to do between August and October last year, only purchasing things like pasta and flour and receiving beef and pork from friends, who are smallholders, in exchange for helping them with their livestock.
"It was hugely successful and great fun, we all really enjoyed it. We hope to do the same thing for six months this year," says Judith, who has given up her job as a GP to expand on the environmental changes.
"We hope to do the same thing for six months this year."
The family will again obtain some of the protein they require from eggs laid by their very own free-range chickens in the back garden.
As Judith explains, they're not the only people who benefit from the six chickens: "Some of our neighbours produce fruit and vegetables themselves and if they have too much, they barter them for eggs.
"One of our neighbours had an internal door that they were getting rid off so we bartered eggs for it because we needed a door. Sometimes neighbours will offer to do work for us for eggs. When the weather is good each chicken can produce six eggs a week."
She adds: "There's usually some kind of bartering going on! It's a good, fun way of working with people."
Tillie and John have also been working with the community in a bid to get the environmental message out.
They have already held two "photovoltaic panel parties" in which they open their doors to locals, provide them with a glass of wine and explain the various changes that they have made to their home and why.
They also plan to talk to pupils at Edie's school in Glasgow later this year about what they can do to save energy, including simple steps like remembering to switch off the lights.
John adds: "We are not just passionate about what we can do, it's about helping other people too – and it can be fun. People tend to feel powerless about climate change and what we are trying to do is help reduce the carbon footprint and say to people, 'you think you're powerless but you are not, and what you do can be significant in what's going to happen with climate change'."