Ms Smith said it was "horrific".
"My child just fell 8m," she said. "I've been told there were some spinal injuries - thank God she wasn't one of them.
"You would think it was safe, with all the health and safety things."
Her daughter, Amelia Peck from Ashhurst, was discharged from Wairarapa Hospital after two hours with a sprained knee, and was back at the showground on crutches.
It was later confirmed all six of the injured children had been discharged from hospital by late Saturday, and that injuries had been largely restricted to cuts and bruises.
Ms Smith said the slide had "just started collapsing".
Amelia, who was part-way up the climbing side, fell on to a tent beside the slide, then to the ground: "I was probably the first one to land. I was in tears, my knee was real sore."
Caleb Larsen, 14, of Masterton, was about to get on to the slide when it started tipping.
"The whole thing caved in ... There was eight people on that side, more people on top. They were all screaming.
"A mate of mine had his nose smashed, he was trying to save the little kids."
Two friends, Riki Edwards and Vinnie Aspinall from Masterton, who were on the slide at the time, said there were "way too many people" on the slide. "There were over 15 people up there," said Riki.
He thinks the weight of a lot of children on one side caused the slide to tip.
"All these kids were falling to the ground, a couple of kids grabbed on to me, a couple landed on me.
"One girl went flying over me, hit me on the head. There was one girl who couldn't walk, I had to help her up."
The slide belongs to Event Fun Unlimited of Waikato, and is called "The Mammoth".
This was the first year the company's inflatable attractions had been used at Masterton A&P show, with Solway Showgrounds cutting its contract with Mahons Amusements, who had supplied fairground rides to the show for more than 60 years.
The owner of the slide, who would only identify himself as Eric, refused to comment until he had spoken to WorkSafe, who are investigating the incident.
"Most of us have kids ourselves - we're pretty concerned about it."
WorkSafe inspector Mark Donaghue was on the scene, but said a formal process would be undertaken and it was too early to make an assessment.
A sign at the start of the slide says "We make it as safe as humanly possible but you ride this entirely at your own risk".
Solway Showgrounds site manager Ally O'Neill said he was "very concerned about the children", but would not make further comment "until the investigation has been completed".
A spokesperson from Wairarapa Hospital said all six children were discharged on Saturday after being "examined top to toe", with none needing to stay overnight.
Masterton A&P Association president Allan Williams said representatives of the show's organising committee had met at Wairarapa Hosital and offered their contact details to the families affected.
Mr Williams said he wanted to give the families "a personal apology" for the incident. "It is such a shame that this has marred what was a very successful and fun day."
Times-Age readers - many of whom saw the slide's collapse - posted comments on Facebook expressing their horror. Several mentioned there was little adult supervision of the slide, resulting in overcrowding.
Another said "someone had stopped the air going into the slide", which led to its collapse.
The slide was one of 16 rides at the show.
