Why didn’t Dr. Hoskins speak up after Noah and the baby’s death ?

Dr. Hoskins doesn't speak up because he has a plan. The morning after the murders, he arrives to take some of Derby's slaves to auction and bring back the money they earn. After several hours traveling in the wagon, Dr. Hoskins pulls off to the side of the road and tells the slaves that he won't be bringing them to the auction. Hoskins is against slavery, and after witnessing the horrible doublemurder the night before, his conscious demands that he help set these three children free. He gives them a small purse of money and promises them a few days head start before telling Mr. Derby that they were attacked by highwaymen and that they escaped. Dr. Hoskins also gives Polly a musket with one round of ammunition, warning her to make that one shot count. The children then run silently into the woods to begin their journey toward freedom.