Dozens of children from Gaza who were due to enter Israel for a two-week vacation were prevented from leaving the Strip by Hamas officials on Wednesday, Israeli officials said. Most of the children were orphans whose parents were killed during Operation Cast Lead. The Kibbutz Movement had sponsored the vacation for 47 children between the ages of four and 13. The children were to be accompanied by five adults from the Strip as well as Arabic-speaking youth movement members from Israel, and were to be hosted in Kafr Kasem, Haifa and Kibbutz Sasa. "Hamas prevented them from leaving today," said Maj.