A mountain rescue team was "horrified" to find children aged two, three and five among a group of nine people who were airlifted to safety from Snowdon.
The group was winched by helicopter from near Snowdon's summit
Seven people from Liverpool and two students from Cardiff were taken by helicopter to Ysbyty Gwynedd in Bangor.
The children were treated for cold, and released from hospital on Wednesday. RAF winchman Trevor Preece said the youngest was lucky to be alive.
Welsh Sports Minister Alun Pugh criticised the adults as "reckless".
"Even though the youngest child was the best clothed she had spent a large part of the time being carried, so in effect it was like wrapping yourself in a duvet and lying outside on the grass," said Flt Sgt Preece.
"When we landed she looked like a rag doll being carried towards me," he added.
He urged people to get expert advice before venturing out on the mountains, but said that even then he would not have taken children out on the walk in those conditions as hypothermia can quickly take hold.
"They are lucky to be alive, the cold will kill you," he said.
Gwyn Roberts, of Llanberis Mountain Rescue, said his team was shocked when they learned the children's ages.
Dr Roberts said the rescue team was alerted at 1720 GMT to rescue the nine-strong group - two couples and their children and two students in their 20s who had joined them on the mountain.
Snowdon is the tallest mountain in Wales and England
The team attempted to reach the group using a 4x4 vehicle but were forced to call in a Sea King helicopter from RAF Valley.
Dr Roberts told the BBC Wales news website: "It's a happy outcome - the kids are going to be fine... but it could have been very different."
He said he was shocked when the team heard there was two-year-old on the mountain in sub-zero temperatures.
He said: "It's very unusual - we were horrified when we had the call."
Welsh Assembly Government minister Mr Pugh, the Clwyd West AM who is also a qualified mountain leader, said there would have been deaths without the rescuers' skills.
He said that "at this time of year, climbing our highest peaks requires winter mountaineering skills rather than simply a pair of boots and a waterproof jacket.
"Without an ice axe and crampons, and the ability to use them, the likes of Snowdon are a potential death trap for the ill-equipped."
Mr Pugh said walkers had to think realistically about the challenge "no matter how tempting the mountains look".
He said: "The group that got itself into all sorts of trouble yesterday was reckless about their own safety and that of their children".