Half of Syria's children have grown up knowing nothing but conflict and at least 2.5 million of them are internally displaced.
Save the Children made the claim in a report released on Monday before a conference on Syria's future to be held in Brussels.
Every minor under the age of 16 has now lived more of their childhood in the shadow of war than outside of it, the organisation said, calling for "a child-focused early recovery in Syria".
"Many children in Syria have grown up knowing nothing but war, seeing and experiencing things that no child ever should. The Syrian children we spoke to feel unsafe and alone after being separated from their family,” Save the Children chief executive Helle Thorning-Schmidt said.
The organisation called on delegates to the three-day Brussels donor conference, which will start on Tuesday, to publicly commit to supporting Syrian children. The NGO wants to see targeted and sustained funding for important sectors on the basis of further consultations with children and young people.
Parties to the conflict and the international community must also take concrete steps to create the conditions for peace and protect children, while ensuring equitable access to basic and life-saving services, Save the Children said.
Many children lost a close relative or have a parent or sibling in detention, missing or disappeared, and thousands have been orphaned or separated from their families as 6.2 million people fled their homes.
Half of the children identified by the UN as in need of humanitarian assistance live in four areas identified as significantly affected by the conflict.
Lina, 13, interviewed in the report, fled the siege in Eastern Ghouta and is now displaced with her grandmother, uncle and younger brother in Idlib.
“We spent the last year in Ghouta in shelters because many schools were bombed. Both of my parents were killed when our house was shelled and I hoped I would follow them, but God had other plans,” she said.
“What is left of my family is my brother, grandmother and my disabled uncle. Now we stay in a house without heating or running water. I wish the war would stop so I can go back to my old house in Ghouta and finish my education and become a teacher. I wish I did not lose my parents.”
Girls and boys are still prevented from accessing safe, quality education as a result of displacement, insecurity, lack of accessible schools and qualified teachers. The psychological distress also has a dire impact on their ability to learn, Save the Children said.
There were differences according to gender, with girls more likely to feel distressed, alone, unsafe and angry.
Incidence of all negative feelings except insecurity came out significantly higher among respondents in north-east Syria than north-west Syria, where a higher proportion of respondents were displaced and more likely to be out of school.
Within the framework of the UN Humanitarian Response Plan for Syria, early recovery focuses on three interrelated themes, namely basic social services and infrastructure, livelihoods, and community security and social cohesion.
Save the Children called on delegates to fully fund the 2019 Syria Humanitarian Response Plan and officially commit to a response that prioritises the needs of children and young people.