Can 'Manche Kinder mögen Äpfel nicht.' be used as a valid german sentence with same meaning?
yes, but 'keine Äpfel' is generally preferable.
Why not with "several"?? I don't get it. ...
I'd translate "several" with "einige", which sounds a bit stronger or more than "some" and "manche".
The way I see it, "manche" is used to point out that there exists at least one