• The group said the South East Asian country was in a "nightmare situation", with the youngest known victim just six years old.
• The deadliest day of the conflict so far came on Saturday, when more than 100 people were killed.
At least 43 children have been killed by armed forces in Myanmar since February's military coup, according to rights organisation Save the Children.
The group said the South East Asian country was in a "nightmare situation", with the youngest known victim just six years old.
A local monitoring group puts the overall death toll at 536.
Meanwhile, ousted leader Aung San Suu Kyi has been charged with violating the country's official secrets act.
Suu Kyi, along with four of her allies, were charged last week, but the alleged crime - which carries a prison term of up to 14 years - has only now come to light.
The new charge against Suu Kyi is in addition to earlier charges of possessing illegal walkie-talkies, violating Covid-19 restrictions during last year's election campaign, and publishing information that may "cause fear or alarm".
The UN's envoy to Myanmar has warned of the risk of an "imminent bloodbath" as the crackdown against pro-democracy protests in the country intensifies.
The warning follows a flare-up in fighting between the army and ethnic minority militia in border areas.
The UN has become the latest organisation to urge the families of its workers to leave but has said that some staff will remain in the country.
The unrest in Myanmar began two months ago when the military seized control of the country after an election which Suu Kyi's National League for Democracy (NLD) party won by a landslide.
When tens of thousands of people took to the streets nationwide to protest against the coup, the military used water cannon to attempt to disperse them. After a week, the response escalated, and rubber bullets and live ammunition were used.
The deadliest day of the conflict so far came on Saturday, when more than 100 people were killed.