I keep thinking this is a phase but it's been going on for about 4 or 5 years now.
Our ds12 is obsessed with history, war, weapons and world domination. On one hand we're thrilled that he has taken such an interest, but it's all he can talk about.
Our daily drives to school are filled with bits of trivia about battles, what kind of weapons they used, who made them, how they were made and how (fill in the blank) tv show was inaccurate. It was cute when he was 7 but five years later I'm growing weary
We don't discourage his enthusiasm but his sister will often yell at him to stop talking about war.
Do your children have one area of study they obsess about? How do you handle it?