pronouns - use of 〜ちゃん as a generic term

In a Shimajiro educational book I saw a line similar to this:

___ちゃんが知ってる乗り物は何ですか？

(the actual one had less Kanji but you get the point)

The question is why was ちゃん used here as a generic term. I thought ちゃん was used more for girls and くん for boys, and since I think the audience for Shimajiro might be more boys, why didn't they choose くん here? Or is ちゃん actually a more neutral term?

Answer

It's common to use ちゃん regardless of their sex when they're are very small... roughly under 6 years old or so.

http://oshiete.goo.ne.jp/qa/983087.html

平均的なところでは，
○未就学児は男女問わず「ちゃん」
○小学生～高校生は男子が「君」，女子が「さん」
○大学生以上の学生，社会人（18歳未満でも）は「さん」
○ただし政治面など硬めのニュースでは男女問わず「氏」