Many parents, as their child get interested in Judaism, worry that their child has joined a cult. Religious cults are a serious concern, especially after events like the armed conflict of the Branch Davidians in Waco, Texas, and the suicide of the Heaven's Gate cult. And considering the way leaders of cults generally take advantage of their members, the fear is not something to be ignored. These are some of the standard effects seen in individuals involved in destructive cults. Do not, however, expect a cult member to show all those symptoms.
Cults never allow their members to ask questions.
Judaism, on the other hand, thrives on questions. Judaism teaches that if you're not asking questions, you're not learning, and you're not growing. The entire purpose of having Rabbis is so that they can answer our questions. Brainwashing relies on keeping the subject ignorant. Judaism heavily stresses study and knowledge.