タイトル通りですが、子供(８歳・娘)が、What a heck・・・を使います。
例：What a heck is that?
我が家では、Fワードはもちろん　SもＡもBワードも使わせません。
小さい子供が使う言葉として　heckは、Hellより　マシだと思いますが、それでも私は好きではありません。
旦那も私と同じ意見だけど　他のネイティブに聞くと　別にＯＫだといいます。
本当は、どうなんでしょう？教えてください。

Correct use: "What the heck ?" or "What the heck is that ?"
"What in the heck is that?"
Don’t say "what a heck". If you say "what", then you must say "the" or "in".
But, you can say:"you played a heck of a game"
"Heck" is the polite form of "hell". It is informal, and used in idioms.
Heck is not a rude word. You can use it in many situations.

-Aaron 　

”一体”何なんだ？
の”一体”とか”一体全体”って感じで　日本語にしても別に悪い言葉ではないし、気にする事ないんじゃないですか？強調の為の語法だと思います。
　

もちろんエッセイなどよりフォーマルな文章の場合は、What in the world is that？などですが、普段の会話などではHeckくらい許してもらわないと、きついとおもいます。 　

I can only understand just a little Japanese, so I can’t read your post.
Can you post again in english?
Yes, "heck" is a form of emphasis. We use it for emphasis.
Anyway, how many (plural or singular) are not important with "heck".
Heck is a polite way of saying "hell" . Hell is a noun that is familiar.
We dont use "a" in front of familiar nouns.
So we say "in hell". We can say: "What in the hell is going on?" or "where in the hell...".
Now, when we say "you played a hell of a game", are we breaking the rule?
Well in this case, hell is a kind of adjective.Think of it as:
"You played a HELLUVA game." This means:"You played a great game."
"Hell" or "heck" can be used also as a proper noun, and in that case you say:
"what in hell" or "what in heck" For example. "What in heck is going on?"

-Aaron