UPDATE: Since this report was published, it has emerged that the civilian shelter or school from next to which the mortar was fired was most likely run by Hamas, rather than UNRWA. The original version, which appears below, had at time of publication been confirmed by multiple and independent sources. The clarification, of course, in no way diminishes from the double war-crime involved in using civilian shelters as cover from which to launch attacks on civilians, which Hamas has made its consistent policy for years.
The mortar round that killed four-year-old Daniel Turgeman earlier today was fired from a United Nations Relief and Works Agency (UNRWA) school, according to security sources.
Ynet reports :
A 4-year-old child named Daniel Turgeman was killed in the evening after being critically wounded in the Sha’ar HaNegev Regional Council by mortar fire during a large barrage of rocket fire from Gaza that also reached central Israel.
Security sources later claimed that the mortar fire that killed Turgeman had been fired by militants from within an UNRWA school in the northern Gaza neighborhood of Saja’iyya.
— Peter Lerner (@LTCPeterLerner) August 22, 2014 
Later reports  identified the site of the mortar launch as Zeitoun, not Saja’iyya.
In other rocket attacks today, a 25-year-old was critically wounded when a rocket landed on an Ashdod street. Earlier today, three people were injured when a rocket hit a synagogue, again in Ashdod . Altogether, 130 rockets were fired into Israel today.
Israel's liaison to the Palestinians said it warned UN/PA/diplomats that mortar fire from UNRWA crossed a "red line" #pt 
— joshmitnick (@joshmitnick) August 22, 2014 
UNRWA facilities have been used to hide Hamas weapon caches and terror tunnels . The continued use of civilian shelters by Hamas has gotten so bad has prompted a bipartisan group of senators to call for an investigation into the ties between Hamas and UNRWA , and has led expert Claudia Rosett of the Foundation for Defense of Democracies to call the UN complicit in terror . Earlier this week, Alexander Joffe and Asaf Romirowsky of the Middle East Forum argued that UNRWA should be dissolved  due to its complicity in terror.