And where they're at, at this Tham Luang cave in Thailand, it's a mountainous area.
Monsoon flooding prevented the group from escaping and from allowing rescuers to find them right away.
Rescue officials are seen near Tham Luang cave in Mae Sai district, Chiang Rai, Sunday. Divers escorted the children, who wore equipment to help them breathe.
Rescuers have suggested that it may take up to two days for the rescue to be completed, with each boy being brought out individually.
The death on Friday of a former Thai navy Seal, Saman Gunan, underlined the risks.
Heavy rain started falling as soon as the four were removed from the cave.
Narongsak said favorable factors for a successful rescue, including the fact that water levels in the cave remain stable even though rain had fallen.
While the names of those rescued have not been released, six of the boys are students at the Maesaiprasitsart School and classmates say they've been closely monitoring the worldwide mission to save them.
"I used to get stuck in Tham Luang cave as well", he said.
'A flash flood because of sudden heavy rain locked them in'.
There had been efforts to pump the water out but those were set back every time it rained.
At some point, there was talk of leaving of the boys in the cave throughout the rainy season, Tracy said.
The current rescue operation is not, Tracy said, "the preferred option". Rescue crews are anxious about the amount of air the trapped children are using, which is being drained rapidly.
Rescue operation commander Narongsak Osotthanakorn made the announcment on Monday afternoon.
The rescue team went into the cave to resume the operation at 11 a.m. (0400 GMT), the chief of the rescue mission, Narongsak Osottanakorn, told a news conference earlier, adding he expected good news.
The world football body Fifa has promised the boys seats at the World Cup final in Moscow on Sunday, but it remains to be seen if they will be well enough to take up the offer.
Governor of Chiang Rai province, Narongsak Osatanakorn, said: "Today is D-Day". Nine people remain trapped in the cave.
The same divers who took part in Sunday's rescue of four boys trapped in a flooded cave will also conduct the next operation as they know the cave conditions.
Authorities spent hours replenishing air tanks along the cave's treacherous exit route.
Officials said that rescue operations could continue for two to four more days. They have not been reunited with their families yet due to infection concerns.
The boys were found inside the cave by British rescue divers a week ago, about 4km (2.5 miles) from the cave mouth.
Adesman said that PTSD is an issue for protracted trauma, and he's optimistic the worst is behind the boys trapped in the cave.
Somboon Sompiangjai, 38, the father of one of the trapped boys, said parents were told by rescuers ahead of Sunday's operation the "strongest children" would be brought out first.
Plans called for the boys to be placed in ambulances and given medical assessments.