The answer is C: Hyperactivity.
Explanation for each option:
A. Seizures: While seizures can be a side effect of some medications, they are not commonly associated with Ritalin (methylphenidate). Therefore, this is not the primary concern for parents to monitor.
B. Gigantism: Gigantism is a condition related to excessive growth hormone and is not associated with the use of Ritalin. Therefore, this is not a relevant side effect to monitor.
C. Hyperactivity: Ritalin is prescribed to help manage symptoms of ADHD, including hyperactivity. However, in some cases, it can paradoxically increase hyperactivity or cause other behavioral changes. Therefore, it is important for parents to monitor for any changes in hyperactivity levels.
D. Bradycardia: Bradycardia, or slow heart rate, is not a common side effect of Ritalin. The medication is more likely to cause an increase in heart rate (tachycardia) rather than a decrease.
Summary: Parents should monitor for changes in hyperactivity when their child is on Ritalin, as it can sometimes exacerbate symptoms or cause other behavioral changes.