hello. im a student in china holding x visa my children with me have s2 visa.

i went to immigration office and they say i have to go back to my country to get s1 for the children im so busy if i go to my country i ll lose my semester.and the children school because go home mean more than one month
my question is if the children overstaying until winter holiday what will happen is it just pay fine or will not let children enter china again
than you