A 2-year-old child comes in to see you with his mother at the GP surgery. The mother tells you that for the past few months, the child has been suffering from diarrhea. On further questioning, she denies that it is foul-smelling but does confirm it sometimes contains undigested food. There are no other symptoms such as abdominal pain or bloating. You plot their height and weight, and it is appropriate for their age. What's the most likely diagnosis?
a) Celiac disease
b) Lactose intolerance
c) Toddler's diarrhea
d) Inflammatory bowel disease (IBD)