Future tense in English as subjonctif présent in French?

Question

"J'ai peur qu'ils ________ des bêtises."

I'm afraid they will be naughty.

(HINT: Conjugate "faire" in the Subjonctif présent)

The suggested correct answer is "fassent"; but why is it not "feront"? Surely, even in French, there is a difference in meaning between "I'm afraid they will be naughty" and "I'm afraid they are naughty"?

Accepted Answer

There is doubt in this statement in French - "fear/uncertainty" that something will (that is 'may') happen in the future. Otherwise the French statement would just be "They will be naughty" or "I know/am sure they will be naughty" - neither of which would be in subjunctive in French, as they are statements of/with certainty. 
In English we do use "I am afraid something will happen" when we mean we "know it will happen", but that is not the case in French.

Answer

Bonjour Harry,
To complement Maarten's answer, follow the link below:
Subjonctif-futur
I hope this is helpful.
Bonne journée !

Answer

Thanks Maarten and Céline for the clarification. How then would you translate:

1. "Whenever Jean visits his grandmother, I'm afraid he is naughty."

2. "Whenever Jean visits his grandmother, I'm afraid he will be naughty."

3. "When Jean visits his grandmother next week, I'm afraid he will be naughty"

4. "Whenever Jean visited his grandmother, I'm afraid he was naughty".

5. "Whenever Jean visited his grandmother, I was afraid he would be naughty".

6. "Whenever Jean visited his grandmother, I'm afraid he was naughty"?

Answer

Confusing indeed, it would mean "future subjonctif?" is there such

Answer

I'm going to answer my own question in part, prompted by Maarten's comment that "In English we do use "I am afraid something will happen" when we mean we "know it will happen", but that is not the case in French."

It's true that in English the phrase "I'm afraid that" sometimes means "I'm sorry to say that" or "unfortunately". If this is the meaning, then in the French translation we could use "je regrette de devoir dire que" (not followed by the subjunctive) or "malheureusement" or a similar phrase. This is clearly the case in examples 1, 4 and 6 above. What do these examples have in common? "I'm afraid" is in the present tense and the following verb is not in the future tense. I'm sticking my neck out to say this is a signal that the translations just mentioned could be used.

Example 5 is the opposite case. "I" clearly was uncertain, and I would expect the subjunctive to follow, except that no one uses the imperfect subjunctive anymore, so I guess the imperfect indicative would be used.

Examples 2 and 3 are ambiguous. You'd need some context to work out whether the present subjunctive or one of the suggested translations with the future indicative should be used.

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