Israel’s goal is to destroy Hamas. Every time they kill innocent children, they create more members of Hamas. Therefore, their goal is any amount of children including 100% of them.
Destroying Hamas means destroying the current leadership, so it can no longer function.
It’s true that Israel is running the risk of inciting hatred and creating more fighters, but those future fighters won’t be in Hamas. They will be in some other organization that replaces Hamas, just like Hamas replaced Fatah.