Local resident Lisa Meehan describes the injuries to the younger victim
Police are questioning two children after an attack that left one boy with life-threatening injuries and another "cut from head to toe".
Officers have been given more time to question the two after an 11-year-old victim was found with head injuries in a ravine near Doncaster.
His nine-year-old friend was found bleeding from knife wounds in a nearby street and has had surgery to his arm.
Prime Minister Gordon Brown said it was "clearly a shocking incident".
Mr Brown said he would be "following the case very closely".
Magistrates granted South Yorkshire Police an extra 36 hours to question the two arrested boys, aged 10 and 11.
Doncaster Council has confirmed that the two arrested boys were recently placed into foster care.
A Downing Street spokesman said that Prime Minister Gordon Brown had cautioned against drawing any wider conclusions about the state of society.
"In his view, the overwhelming majority are well-behaved and have good upbringings, and therefore he would be cautious about reaching any general conclusion about what is a disturbing but singular event," the spokesman added.
Local residents told BBC News they believed the two victims had been hit with a brick, slashed with a knife and burned with cigarettes in the Brick Ponds area of Edlington on Saturday.
It is thought their mobile phones, trainers and about £3 in cash were stolen.
Lisa Meehan said her daughter had found the younger victim wandering in the street barefoot and covered in blood.
Jean Wright explains how her son found the 11-year-old victim
"I felt sick to my stomach," she said. "You couldn't see his face, he was cut from head to toe with a gash across his head.
"They had slashed his arms and face and he had no trainers or socks on. His face was mashed."
Resident Jean Wright, 68, said: "My husband saw [the younger boy] walking past the outside of our house and he was covered in what my husband thought was red paint. When he went out he saw it was blood."
Derek Wright, 70, said his son Ian had seen the 11-year-old on the edge of a stream, lying face down with his arms outstretched. He was covered in dried mud and blood, he said.
Mr Wright added: "They're animals, absolute animals. How any child could do this to another child I don't know."
The younger boy has had surgery on his arm at Doncaster Royal Infirmary and the older boy remains in a critical condition after being airlifted to Sheffield Children's Hospital.
Officers from South Yorkshire Police have been carrying out house-to-house inquiries to try to establish what happened.
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