A police tent covers the scene where one of the boys was attacked
Police are continuing to question two children after an attack that left one boy with serious injuries and another "cut from head to toe".
Officers have been given an extra 36 hours 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 nearby and is set to undergo a second operation.
The 11-year-old's family said they were grateful for the community's help.
In a statement the family said: "We would like to thank all the community for their help in finding our son and for all their continued support through what is a very traumatic time.
"We are hoping that our son will continue to recover from his ordeal."
Doncaster Council confirmed the two arrested boys were in foster care.
The BBC's Chris Buckler in Edlington
If the old quarry where the boys were attacked was once a play area, it is now clearly a crime scene.
Old uprooted bushes hold police tape in place at the bottom of a hill. It was here that the 11-year-old was found unconscious.
The nine-year-old had managed to wander into nearby streets covered in blood. That image is still being talked about there and on every street corner of this old mining town.
Residents question how it could happen and who should be held responsible.
At a nearby allotment, a man claimed that people had become used to vandalism and nuisance crime - but he said violence that would leave children seriously injured was simply unthinkable. Until now.
Prime Minister Gordon Brown said on Monday it was "clearly a shocking incident" and he would be "following the case very closely".
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.
The younger boy has already had one operation on his arm at Doncaster Royal Infirmary.
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.
SATURDAY'S INCIDENT, EDLINGTON, SOUTH YORKSHIRE
Nine-year-old boy found injured on Auburn Road
Critically injured 11-year-old found
Two boys, aged 10 and 11, arrested