How to pronounce “unassailably” in English

So my second book, for example, has a nine-year-old who does quite a bit of the narrating.If I were to go to a playground and take dictation from a nine-year-old, I would have an unassailably realistic portrait of a nine-year-old-- a journalistically accurate one.But if you were to then read that, you might think either, this is boring, or it just doesn't sound like a nine-year-old to me.