Teddy's Button by Amy Le Feuvre

Teddy loves to tell the story of how his father heroically died on the battlefield. He wants to become a soldier just like him. But this brings contention and strife when a new girl comes to town. Nancy is just as selfishly proud as he is and from the beginning, they are enemies. Yet as time passes, they learn to put their prejudices to the side, allowing a new friendship to bloom.