Why not: "they are waiting for the fourth child"? What suggests here that it is about expecting a child?
Čekají čtvrté dítě. = 'They are expecting their fourth child.'
Čekají na čtvrté dítě. = 'They are waiting for the fourth child.' čekat na + acc = 'to wait for sth/sb'
Ceska veta nerika nic o tom jestli cekaji "jejich" dite... proto nevidim duvod proc do anglicke davat "their"
Tím důvodem je angličtina. Prostě to tam patří.
They are waiting the fourth child was marked wrong why?
And so now... what's wrong with they are expecting the fourth child??
"They are expecting the fourth child." is not possible?
I don't think so.
could i insert jejich for their ?
Yes, you could, but it wouldn't sound very natural. "Své/svoje" would be better than "jejich." Nevertheless, it sounds the best if omitted.