Hi Louisa, Welcome to HealthcareMagic Forum.
Kindly do not worry, as Bowel cancer
is not common in children. It it were black it is calles Melena if they were red it is called Hematochezia
. The exact for this has to be ruled out as it could be due to Hemorrhoids, constipation, Milk allergies, trauma or Vascular malformation
which are abnormal collections of blood vessels called arteriovenous malformations. Kindly take her to a Pediatrician
so that he/she can examine her and rule out these causative factors.