On year 14 Sarah has an obvious pregnant belly and then the next scene States 17 years which would be three years later she was pregnant again. Correction: She was pregnant with a fourth child which was stillborn.
Thomas is born after 7 years of captivity, when the film gets to 17 years of captivity Thomas would be around 10 years old however he is clearly far older.
When the police officer is investigating Sarah's "disappearance", Chris' name and as person who last saw Sarah. When The officer says he wants to go talk to him, Amy says she's going to get Chris' number. The cop then leaves the house before Amy can come back with the phone number, an important lead when conducting an investigation. When Chris comes to bring Sarah the motorcycle helmet, he mentions to Don that the police did question him.