There are several synonyms for the phrase "kept in." One alternative is "confined," which means to keep someone or something within certain limits or boundaries. Another option is "controlled," which refers to the act of managing or regulating something or someone. "Contained" is another synonym, meaning to keep something within certain limits or boundaries to prevent its spreading or escaping. Additionally, "restrained" is another viable synonym, suggesting that force or power is used to hold something or someone in check. Other alternatives include "restricted," "locked in," "enclosed," and "penned up." Each of these synonyms captures the essence of being "kept in".