Common Sense Note
Parents need to know that there's abundant gunplay (rifle fire) as the Colonial militias face the British Redcoats, with some extras falling dead in both direct confrontation and sniper-style fire. The young hero burns his hand in molten silver, a vivid trauma in the book for generations of young readers, handled more discreetly here (the crippled limb isn't even shown in closeup). An ultra-religious character comes across as stern and domineering, but not cruel. The Esther Forbes novel is still required reading in many schools; kids today might be tempted to watch the movie instead of doing the reading.
War-conditions shooting, with dead/wounded bodies, but no blood or gore. Johnny famously sears his hand in molten silver, but it's not graphically depicted.
Early Revolutionary War lessons here include an oratory that this is to be the start of a long, hard campaign, not just a party throwing tea into Boston harbor, and that there are serious issues at stake in the uprising. One character is depicted as a strict Puritan type, whose stubborn religious streak leads to Johnny T's fateful wound. Unlike later Hollywood views of Christians, he's not hateful, and no comparison is made between his conservatism and the views of the rebel Boston patriots.
Drugs / Tobacco /
Mention of pubs and some pewter mugs sitting around, probably not filled with milk, but nothing shown.