Apologies for this basic question:
Why does 'детей' in 'сколько у тебя детей' appear in the gen. and not the nom. as in the usual у + gen. + nom. construction?
I wanted to ask this question as the preceding sentence read: 'у тебя есть дети' where the у + gen. + nom. seemed to work perfectly. Is it because
- (1) the 'existence' of the children is no longer in question;
- (2) that the noun [детей] must agree with the personal pronoun [тебе] in the genitive case; or
- (3) because we're now asking about the quantity of children?
Apologies, I just really want to know for sure. If anyone could explain exactly why it changes I'd be very grateful - thanks!