**Core Concept**
The child's symptoms and EEG findings are indicative of absence seizures, a type of epilepsy characterized by brief, sudden lapses in consciousness. The 3 per second spike and wave discharge on EEG is a hallmark of this condition.

**Why the Correct Answer is Right**
The first-line treatment for absence seizures typically involves the use of anticonvulsant medications, such as ethosuximide, valproate, or lamotrigine. Ethosuximide is particularly effective in reducing the frequency of absence seizures. However, one anticonvulsant medication that is not indicated in the treatment of absence seizures is **phenytoin**. This is because phenytoin is more effective in treating tonic-clonic seizures and partial seizures, but it can actually worsen absence seizures.

**Why Each Wrong Option is Incorrect**
* **Option A:** Ethosuximide is an effective treatment for absence seizures, making this option incorrect.
* **Option B:** Valproate is a broad-spectrum anticonvulsant that is often used to treat absence seizures, so this option is incorrect.
* **Option C:** Lamotrigine is another effective treatment for absence seizures, which makes this option incorrect.

**Clinical Pearl / High-Yield Fact**
It's essential to note that absence seizures often have a good prognosis with treatment, and most children can achieve seizure control with medication. However, it's crucial to differentiate absence seizures from other types of seizures, such as tonic-clonic seizures or complex partial seizures, as the treatment approach may differ.

**Correct Answer:** D. Phenytoin.