Despite the series taking place from December 1774 to May 1787 (a total of twelve years), James, Henri, Sarah and Moses don't seem to age at all.
From August through September, the characters are in two places at the exact same time. James and Henri are present to witness LaFayette's courage at Brandywine on 11 September 1777, yet are also with General Gates' American army at Saratoga (and James is a prisoner of the British during that Saratoga episode at the same time he's able to witness Brandywine).