Complex sentence: Lack of sanitation contributes to approximately 700,000 child deaths every year due to diarrhea, and chronic diarrhea can have a negative effect on child development (both physical and cognitive).
Split into simpler sentences: Lack of sanitation contributes to approximately 700,000 child deaths every year due to diarrhea. Chronic diarrhea can have a negative effect on child development (both physical and cognitive).