Learn Hardcore Japanese: kazoku ha maitosi haru ni bizyutukan wo otozuremasu. - My family visits an art museum every spring.

は marks the topic of the sentence—what you’re talking about—and sets up “(my/their) family” as the context for the action. Using が would present 家族 as the grammatical subject and often adds emphasis or introduces new information, which changes the nuance.

Can I specify whose family it is by adding 私の before 家族?

Yes. 私の家族は毎年春に美術館を訪れます explicitly means “My family visits museums every spring.” Without 私の, 家族 relies on prior context to indicate whose family you mean.

Why is 春 followed by に?

Seasons are time expressions in Japanese and generally require に to mean “in [season].” So 春に means “in spring,” just as ３月に means “in March” or 金曜日に means “on Friday.” (Some time words like 今日/明日 don’t take に, but seasons do.)

Why is 美術館 followed by を instead of に?

The verb 訪れる (おとずれる) is transitive and takes its direct object with を. You “visit” a place as an object (美術館を訪れる). If you used に with 行く, you’d be marking a destination (“go to the museum”), but here the focus is on the act of visiting.

What’s the difference between 訪れる, 訪問する, and 行く?

訪れる (おとずれる): neutral/formal verb for “visiting” places or events.
訪問する (ほうもんする): more formal/official, also used for visiting people or organizations.
行く: “to go” somewhere, emphasizing the movement rather than the visit itself.

Why are 毎年 and 春に placed before the verb, and can I switch their order?

Japanese places time expressions before the verb, but their internal order is flexible. You can say 毎年春に or 春に毎年 without changing the meaning, though general-to-specific (毎年 → 春に) often sounds most natural.

How do I make this sentence casual instead of polite?

Change the verb from the polite ～ます form to the plain form:
家族は毎年春に美術館を訪れる。

How do you read 毎年 and 訪れます?

毎年 is usually read まいとし (though まいねん appears in some dialects).
訪れます is read おとずれます (the polite form of 訪れる).