Strikes in multiple neighborhoods across northern Gaza today have killed 42 people according to Gaza's Civil Defense. Videos from the immediate aftermath of the strike show an entire building leveled, children covered in dust.

A bombing of Al-Shati camp killed 24 people, a bombing in Al-Tufaah killed 18 people -- the number of casualties is likely to increase -- and a bombing in Al-Zaytoun killed 7 people, according to Civil Defense.

Fifty others were injured in the attacks, according to the Hamas media office.

Several others are still trapped under the rubble.

The Israel Defense Forces told ABC News they struck two Hamas military infrastructure sites in Gaza City.

The number of children who are missing or separated from their families in Gaza may be as many as 21,000, according to humanitarian aid group Save the Children.

This organization -- which has been providing support for Palestinian children in the region since 1953 -- reports that likely 17,000 children are unaccompanied and separated, and another 4,000 children are likely buried under the rubble based on data from the United Nations and the Hamas-run Ministry of Health in Gaza.

"Children who are missing but living are vulnerable, face grave protection risks and must be found. They must be protected and reunited with their families," said Save the Children’s Regional Director for the Middle East Jeremy Stoner. "For the children who have been killed, their deaths must be formally marked, their families informed, burial rites respected, and accountability sought."

Click here to read more.

-ABC News’ Kiara Alfonseca