Marking for reference, this updated article from earlier today that has a list of the children and their specific details:

The children and babies kidnapped on October 7 and held hostage by terrorists in the Gaza Strip. (Israel's official Twitter account)
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Eta, this is the second time I’m seeing this, “
Not all of the Israeli children in Gaza are being held by Hamas, the main Gazan party to the deal, and not all of their whereabouts are known.”
* I saw something else that said something like that, not all being held by Hamas…who else would they held by? I know it said some hostages may be with Palestinian crime families, etc., but it almost possibly sounds like there’s another affiliated group, “the
main Gazan party to the deal.” Idk. Maybe I’m just reading it weird.