They said his room had more Thomas The Tank Engine merchandise than a toy store. Train duvet covers, posters, lampshades - you name it.
On Saturday, when the Kingston Flyer was fired up for its second season since being mothballed for nearly three years, it was no wonder his eyes glinted with excitement and his smile lit up the restored 1927 carriage he sat in with his parents.
Xavier was too young to say what his first ride meant to him.
He didn't need to. His scream of excitement at the departure whistle said it all.
"It's a good project. It is really nice to bring back that golden age ... and remind people of the past."
The family travelled to Kingston for the first ride of the day at 10am, along with 160 others.
The second ride to Fairlight carried 282 and excited owner David Bryce called at the end of the day and announced there had been an overwhelming 611 passengers for the day.
A year ago, when he bought the train, it was hard to get a word out of Mr Bryce. On Saturday, he said: "I'm not a softy at heart".
He might not be, but on Saturday he stayed behind from the first ride to talk about his new favourite toy and, like Xavier, his eyes lit up when he did so.
"I've achieved what I wanted to achieve. I've been in my own little world down here for the winter.
"I've got a soft spot for this train."
He confessed he had never been a train enthusiast and was quite happy running his vineyard in Marlborough before the Flyer came up for sale midway through last year.
He admitted he missed a home he had only visited for two weeks in the past 12 months.
On Saturday, he received the reward for all that hard work when friends of the Flyer gathered from far and wide to celebrate with him. Many thanked him for getting it back on track.
"It's very humbling.
"It's emotional; it's an emotional experience. Seeing the children and the excitement for all these people, that's the reward."
There was not a lot of difference between Xavier's naive excitement the train owner's.
A realist might ask the 611 travellers of Saturday: "Why fill the car with petrol to drive to Kingston just to ride 25km to Fairlight and back again, there's no logic.
Surely, the 16,000 passengers who rode on the train last season would disagree.