The Law of Return gives every Jew and his family members the right to obtain the status of a repatriate and an Israeli citizen. The great-grandson/daughter of a Jew (fourth generation) is not eligible for immigrant status or Israeli citizenship If a Jew applies for repatriation to Israel under the Law of Return along with their fourth grandchildren up to the age of 18.
Read the full article on government websites: Israeli citizenship for fourth generation grandchildren.
The Ministry of Interior offers the opportunity to regulate the legal status of the minor in Israel, under the Entry Into Israel Law, in order to allow the family to remain united.
If not, so there are other procedures to obtain citizenship to Israel