Final answer:
A nurse should teach parents about the potential side effect of gingival hyperplasia when their child is prescribed phenytoin for seizure control. Gingival hyperplasia is an overgrowth of the gums, which requires good oral hygiene and regular dental visits to manage.
Step-by-step explanation:
The nurse teaching parents of a child prescribed phenytoin for seizure control should include gingival hyperplasia as a potential side effect. Phenytoin is an antiseizure medication, and while it can be effective in the control of seizures, it has several side effects that patients need to be aware of. Gingival hyperplasia is an overgrowth of the gums, which can occur after taking phenytoin for a period of time. It is important for patients to practice good oral hygiene and visit the dentist regularly to manage this side effect. Side effects such as insomnia, hypertension, and increased appetite which are listed in the question are not the typical side effects associated with phenytoin use.