The verb form יושן is very controversial, in some linguistic communities it is very common, in others it is considered an abomination. In fact there is nothing wrong with it, but if you want to make sure that you not only are correct but you also sound correct to everyone, use ישן.
definitely the abomination. The יושן form is used as an imitation of baby talk. Don't use it at all.
Let's agree to disagree. To me, language is what people speak, and there are differences between different communities. The Hebrew Academy is not the language, it's just a bunch of people.
Literally translated this reads "the man sleeps while that the children eat. Is the ש in שהילדים extraneous?
No. A literal translation is: The man sleeps at the time that the children eat.
The shin is necessary.
How does this use of בזמן differ in meaning or tone from if כש were used instead