One child was killed and two others were wounded when a rocket landed on their home in the Egyptian town of el-Mattallah south of Rafah, near the border with Gaza, security and medical sources told Reuters late on Wednesday.
Sara Salama, 13, died while her brother Khaled, 8, and sister Rahaf, 2, sustained serious injuries and were taken to hospital.
The rocket impact is the third to hit the area in recent weeks, security sources said, adding that Egyptian authorities were investigating the incident.
Israeli police said a rocket fired from Gaza landed in Israel on Wednesday evening. Gaza's ruling Hamas denied any had been fired from the territory.
Egyptian security forces have been struggling to quell an Islamist insurgency in Sinai that has killed scores of soldiers and policemen.
The violence surged after the army overthrew Islamist president Mohamed Mursi last year and the militants extended their reach to Egypt's mainland with a series of bombings, prompting the army to intensify its attacks on them in Sinai.