Complex sentence: There are two audition days so children who are sick the first day may make it up the next day, or vice-versa; if the auditioning child is well both days, they are expected to attend both.
Split into simpler sentences: There are two audition days so children who were sick the first day may make it up the next day, or vice-versa. However, if the auditioning child is well both days, they are expected to attend both.