If your options are:
A. High rate of homeschooling
B. Lack of knowledge of disease
C. Junk food
D. Children's lack of exercise
Then, read the following:
___________________________________________________
The factor that plays the biggest role in delaying the detection of childhood diseases would be the lack of knowledge that the disease(s) even existed. If one lacks awareness/knowledge of the present diseases, they may not be able to identify early symptoms or seek early treatment for the disease. Hence, Option B) Lack of knowledge I'd say would be the biggest factor out of the given options.
Hope this helps!