Responses

It's a matter of the child's knowledge and preference. Usually kids aren't taught that one can have two dads. His general knowlege says there only papa and mama. So if daiki is "papa" then minjoon must be "mama" even if he is a man. Even if you teach him to change his way of calling he prefers the word "mama" . By the time the child grew older will then he will call minjoon "dad".
can't toma also calls him dad or smt ╥﹏╥