At least one of your examples seems similar to interrogatives like:
- "Did you stop beating your wife?"
- "Do your parents know you're gay?"
The first question presumes or presupposes that you used to beat your wife. The second sentence presumes or presupposes that you are gay. If you answer 'yes' or 'no', you're tacitly affirming these presumptions.
These are called loaded questions, "a question that contains a controversial or unjustified assumption" (here).
At least one of your examples is a loaded question:
- "Why are nightmares more common in children than adults?"
Regarding your other sentences:
- "Because the official language of the USA is English, it should be the priority in schools".
(4) is not a loaded question. It's not even a question. It just has a false antecedent.
- "How do humans know when they're being watched?"
(5) does not presume that humans are being watched. It's a straightforward question asking how do humans know they are being watched, when they are being watched. There is no fallacy or unjustified assumption here, as far as I can see (except maybe suggesting that some humans do know when they are being watched).
The general name for an implicit assumption which "sits behind" a statement is presupposition. A presupposition is a proposition which is not expressed by a sentence but which is taken for granted in some sense. The speaker of the sentence is committed to its truth.
For example, if I utter:
- "Obama stopped smoking."
I'm committed to the truth that Obama used to smoke. That Obama used to smoke is a presupposition of (6). (6) presupposes that Obama used to smoke.