More than 300 videos were submitted to Farmers — and Reid's older brother, Baxter, 8, was also in the mix.
Mum Kirsty Mortensen said Reid's selection was "quite a cool achievement for a 5-year-old, and my 8-year-old handled it like a boss".
Mortensen said Reid had the personality and funny little mannerisms to make his videos work.
"It's just the way he is. And his ad-libbing — he just injected his personality into the video."
There was no practice run — the submitted video was the first take.
Farmers marketing campaign co-ordinator Nathan D'Mello said it wasn't easy to select the 12 Toy Squad members but Reid was entertaining "and we thought he'd be a really good match".
Those on the selection panel were looking for personality and the way potential testers talked about their toy.
"We had an amazing reaction from it and got some great kids."
Reid's first review, of a Really Rad Robot, is due to be posted on the Farmers website this week.
Reid said he liked the robot because it was blue, "my second favourite colour" (red is his favourite).
"It's a good toy," he said. And it was "pretty cool" he got to keep it.
Reid was a bit nervous doing the video but was now excited and felt happy with himself for being selected.
Farmers merchandise manager Rob Taurima said the concept was about trying to increase engagement with consumers.
"We know YouTube videos around this type of content are really popular with kids of that age, so it made sense to produce something in a format our customers want to see."
Toys Taurima expected to be top-selling stocking stuffers included the LOL Surprise range and Razor Turbo Jetts.