Video report by ITV News Correspondent Dan Rivers - warning: contains disturbing images
The organisations confirmed at least 33 children have been killed since June 24, compared to 31 children killed during all of 2018 but local hospitals runs by The Syrian American Medical Society (SAMS) put these figures at double.
Figures released by SAMS show 175 children have been killed since April 26 and 827 children have been admitted to hospital in north-west Syria in the same time period.
This week has been the deadliest since fighting escalated in north-west Syria, with the violence killing eight children on Monday alone.
The escalation in violence, which started at the end of April, has left at least 400 people dead, another 440,000 civilians displaced.
One SAMS doctor working in south Idlib, who wanted to stay anonymous, told ITV News: "There has been continuous bombing in Idlib for almost three months now.
"This week one massacre caused more than 100 casualties and at least 30 were children. The medical staff are working under stressful conditions as health facilities are targets for airstrikes."
Relentless airstrikes and multiple bombings have inflicted horrific injuries on victims, many of whom are women and children. ITV News filmed in one hospital where three young girls were fighting for their lives.
Authorities are still recovering bodies from the rubble – some burnt beyond recognition.
One eyewitness, Ahmad, said he had seen victims "torn to pieces".
“The bombardment is relentless. It seems as though the different sides have stopped fighting each other and are fighting us, civilians, now,” he said.
“It’s just senseless brutality.
"I saw dozens of people killed in the marketplace, torn to pieces, including many young children who were playing on the street.
"They should have been safe."
Sonia Khush, Save the Children Syria response director, called the situation in Idlib a "nightmare".
“The children of north-west Syria have been caught in violent conflict for 80 days with no lull," she said.
"They have been denied education, food, and healthcare, and forced to sleep under the trees in open fields for months now."
In the last two weeks, at least four medical facilities have been impacted by the violence, as well as a water station serving more than 80,000 people, and several schools, settlements for displaced civilians, markets and bakeries, according to the UN.
In the last two weeks, at least four medical facilities have been affected by the violence, as well as a water station serving more than 80,000 people, and several schools, settlements for displaced civilians, markets and bakeries, according to the UN.
The Syrian American Medical Society said many medical facilities have suspended their operations, while some are operating under a state of emergency.
Eight water facilities have been attacked in the last two months, diminishing sources of safe drinking water for 250,000 people in southern Idlib.
In the northwest, at least 44 schools have been damaged or destroyed recently, as attacks on educational facilities and personnel have increased.
Many displaced civilians had been heading to north Idlib as it is the closest they can get to Turkey.
However, violence in the region has also intensified after forces fighting against the Syrian government - a mixture of rebels and Jihadis - made their way north as a last-ditch effort for their cause.
Syrian and Russian forces have followed, hoping to quash opposition against President Bashar al-Assad's regime.