Neville is eight when he stops believing in God.
Growing up, he needed someone to bargain with: Let me understand this lesson, and I won't read comics under the covers. Let Gran have cake for tea, and I won't fidget. Let it not rain, let me win this game, let me have magic. Let my parents recover. Let my parents recover, and I'll do anything.
When Uncle Algie drops him from a window and he bounces, Gran is determined to go to St. Mungo's and inform Frank and Alice of the good news.
Neville is sure his newfound magical abilities are a miracle. If God interceded once, surely He will do so again.
Let my parents recover, and I'll do anything.
He sees his mother's eyes lighting up in recognition and hears his father calling him 'son'. The dearly held dream is possible, is probable, it will happen today. He's sure of it.
Leaving the hospital, he disobeys Gran and slips the bubblegum wrapper into his pocket for the first time. He doesn't believe in God anymore.