It added that the Aleppo neighborhoods hit were Jabal Badro, Tariq al-Bab and Ard al-Hamra. The fourth strike documented by the group was in Tel Rifat, north of the city.
UNICEF said in a statement that it is "appalled" by the deaths of children, and called on all parties in the conflict to "ensure that civilians — and children especially — are protected, at all times."
U.N. political chief Jeffrey Feltman condemned the bombings in Aleppo and Damascus and repeated a call "to immediately end the supply of arms to both sides in this brutal conflict." He pledged that "perpetrators of serious crimes will be held accountable."
Syria has never acknowledged the strikes, and portrays the conflict as a foreign conspiracy carried out by "terrorists" to weaken the country.
The missile attacks have outraged the leaders of Syria's exiled opposition who have accused their Western backers of indifference to the suffering of civilians caught up in the conflict.
Also Tuesday, the Observatory said the death toll in a car bomb attack in Damascus had risen to eight. All were regime security officers, it said.
The blast late Monday struck a security checkpoint in the neighborhood of Qaboun, less than a kilometer (mile) from Abbasid Square, northeast of downtown. It was followed by several other smaller blasts thought to be mortar shells landing in various districts of the capital.
The explosions and subsequent gunfire caused panic among residents who hid in their apartments.
Syria's state news agency said the blast was caused by a suicide car bomber and caused an unspecified number of casualties.
The U.N. says some 70,000 have been killed since Syria's conflict began in March 2011.
Associated Press writer Ryan Lucas in Beirut and Edith M. Lederer at the U.N. contributed.
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