More than 76,000 children in Myanmar have been forced to flee their homes since the coup, Save the Children said in a statement.
Most of the displaced children are living outside in the jungle, with nothing but tarpaulins held up with bamboo sticks to protect them from the torrential monsoon rain.
Many families do not have adequate food supplies and are sharing just one meal between them per day, Save the Children said.
Since the coup, 206,000 people have been displaced across the country.
In Kayah State in southeastern Myanmar, around 22,000 people fled their homes in September alone, according to the UN.
More than 79,000 people – including around 29,000 children – are currently displaced in the state.