- The fluoride content in children's toothpaste is typically lower (around 500 ppm) compared to adult toothpaste (approximately 1450 ppm) primarily to minimize the risk of dental fluorosis.
- Dental fluorosis is a condition that results from excessive ingestion of fluoride during the formative years of the teeth, leading to changes in the enamel appearance such as white streaks or, in severe cases, brown staining and surface irregularities.

- Children are more likely to swallow toothpaste rather than spit it out, especially those under 6 years old.
- Because of this, having a lower fluoride concentration helps reduce the total fluoride intake from toothpaste, thereby decreasing the risk of fluorosis while still providing enough fluoride to protect against dental caries.

Other options are less relevant because:
- While children have developing teeth, the primary concern is safe fluoride intake rather than reduced fluoride requirement per se.
- Saliva flow differences in children do not significantly impact fluoride retention in a manner requiring lower fluoride concentrations.
- Oral mucosa irritation from fluoride is uncommon and not the main factor for reduced fluoride levels in children's toothpaste.

In summary, the key reason for the lower fluoride concentration in children's toothpaste is to balance effective caries prevention with safety, primarily by minimizing the risk of dental fluorosis due to accidental ingestion.

Reference: Fejerskov O, Kidd E., Dental Caries: The Disease and Its Clinical Management, 3rd Edition, Chapter 7, pp. 152-155