2:1 civilian:Hamas ratio according to the IDF, with 5000 from Hamas dead and 10,000 civilians dead [0]; Gaza’s population is about half under 18 [1].
So if you figure deaths among civilians are random, then about 5,000 Gazans under 18 are dead.
[0] - https://edition.cnn.com/2023/12/05/middleeast/israel-hamas-m...
[1] - https://www.npr.org/2023/10/18/1206897328/half-of-gazas-popu...
From [0]:
>The Israeli military has not officially published any estimates of those killed.
> The AFP news agency first reported the Israeli assessment on Monday, citing a briefing for foreign media by senior Israeli military officials. Asked about reports that about 5,000 Hamas militants had been killed since October 7, one of the officials replied, according to AFP: “The numbers are more or less right.”