They were supposed to be safe. Bahaa Abu al-Ajeen was walking his 3-year-old son, Rayan, back to the tarpaulin-covered shack they called home, a makeshift dwelling providing some shelter from the sun on a war-ruined farm in central Gaza . The pair walked in what was designated as a safe area for civilians close to the “ yellow line ,” a boundary marked with yellow blocks and flags that divides Palestinian-controlled parts of Gaza from areas under Israeli military control. But al-Ajeen, 38, said