Nine people, including children aged two, three and five, have been airlifted to safety from Snowdon.
The group of four adults and three children from Liverpool and two students from Cardiff was taken by helicopter to Ysbyty Gwynedd in Bangor.
The children were treated for the effects of cold, but were due to be released from hospital on Wednesday.
Gwyn Roberts, of Llanberis Mountain Rescue, said his team was "horrified" when they heard the children's age.
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.
By the time 999 was called, the youngest child had stopped crying, which is a bad sign
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 and I believe they are due to be released from hospital.
"But it could have been very different."
He added 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.
"The youngest child was in a back carrier and was becoming quite cold.
"If children are being carried, they are not generating any heat and can succumb to hypothermia.
"By the time 999 was called, the youngest child had stopped crying, which is a bad sign."
Dr Roberts said there was "some pretty poor decision making by the group" who had not taken a torch or map up Wales' highest peak, while one of the students was wearing trainers.
He added: "They set off quite late in the day - at 1pm - and were close to the summit when they realised it was icy and the children were crying.
"They decided to carry on to the summit and get the train down - however, the train is not running at this time of year."
The group reached the summit at 1645 GMT and tried to follow the railway back down the mountain before calling 999 at about 1700 GMT.
Dr Roberts said the group had been irresponsible and were "extremely lucky".
He added his team receives a higher number of call-outs during school holidays.
He said: "We would like to get across the message that the mountains are extremely icy, even if there is not much snow.
"We would also urge people not to take young children into the hills."
Story from :
BBC NEWS
Published: 2006/02/22 22:02:31 GMT