Too young; the Longbottoms were tortured right after James and Lily had died, so Neville wasn’t much older than Harry had been... While being forced to watch as your parents were tortured to insanity is a horrible, terrible thing, so is watching your mother be murdered in front of your eyes, and watch as her murderer raised his wand against you too. But if Neville doesn’t remember it, was too young to truly comprehend it, then maybe Harry doesn’t remember either. Maybe Harry is being raised a happy, healthy boy, and being taken care of by a loving family.