Medics said Israeli gunfire directed at a tent encampment on the eastern side of the al-Bureij refugee camp in centre of the territory killed nine-year-old Tala Abu Matar.
The Israeli military said it was not aware of the incident.
An air strike at a metal foundry in Gaza City's Sabra neighbourhood killed four people.
Witnesses said the site was hit with three Israeli missiles.
Israel's military told Reuters it had struck "terrorist" infrastructure, without giving further details.
Separately, the military said that since Thursday its forces had killed at least two Hamas fighters in the north of the Gaza Strip who were planning attacks on its troops.
Later on Sunday, an Israeli strike at a tent encampment in the Mawasi area of Khan Younis, in the south, killed at least one person and wounded several others, including children, medics said.
Israel's military did not immediately comment.
The ceasefire agreed in October 2025 between Israel and Hamas halted major fighting in the strip but it has failed to stop Israeli attacks that have killed more than 1000 Palestinians since it took effect.
Four Israeli soldiers have been killed by militants in the enclave over the same period.
The latest violence comes as Hamas leaders visited Cairo for further talks over implementing the second phase of US President Donald Trump's Gaza Strip peace plan.
The discussions include Hamas disarmament and Israeli army withdrawals, according to sources close to the talks, adding that there had not yet been a breakthrough.
Nearly all of the Gaza Strip's two million people, most of whom have been displaced several times, live on a tiny strip of land along the coast, mainly in makeshift tents or damaged buildings, under Hamas control.
Hamas-led fighters killed 1200 people during their cross-border attack into Israel on October 7, 2023, according to Israeli tallies.
The Gazan health ministry said more than 73,000 Palestinians have been killed in the territory since then.
