Farewell letter in Japanese to a little sister


I am going to leave Japan soon and I need to say farewell to many people. One
of the people I know is a little girl who is about 6 years old. She is very
cute and very close to me during the time I stay here in Japan. Now, I want to
write a letter to her to say goodbye as well as to tell her to be healthy,
that I will remember her for a long time. I am really not sure how to write it
properly in this case. Because I think I should use informal Japanese, just
like a brother talking to his sister. I have learned Japanese for a while but
mostly in formal and respectful forms like masu, desu.

Can you give me some guidelines for writing this letter? How should I express
myself in the letter (boku, ore, watashi?), how should I mention her (anata,
A-chan)? What useful phrases I can use here?




I think children of about six years old can't read kanji, so you should write
the letter in hiragana.

If you are female(male), you should use ～のおねえさん(～のおにいさん) when you explain
yourself. For example, if you are from the U.S, you can say アメリカのおねえさん(おにいさん).
You can call her (first name)ちゃん. And you shouldn't use difficult words. If
you draw some easy pictures in the letter, she may be pleased.

For example,

> (First name)ちゃんへ
>
> ～のおねえちゃんは、じぶんのおうちにかえるね。～ちゃんとあそべてとてもたのしかったよ。またあそぼうね。げんきでね。バイバイ。
>
> ～のおねえさんより

