"Jsou tak chudí, že se nemohou starat o své děti."

Translation: They are so poor that they cannot take care of their children.

[garpike]

I got this sentence seven times in the same lesson (Modals 1, 1), all in the form of a 'fill in the blank' question, with 'nemohou' removed.

[VladaFu]

You will have to complain somewhere else. The contributors of this course can only add more sentences but they cannot control how the questions for you to answer are chosen. Only Duolingo developers can perhaps control that.

[NinaOBel]

I think that this topic has less sentences then Duo wants.

[snikta]

can this also be translated as 'They are so poor that they cannot take care of their own children' (which is a common expression in British english) ?

[VladaFu]

their own = své vlastní

[Artashes98]

Is the second 'they' really necessary in English? "They are so poor that cannot take care of their children."

[garpike]

That would mean that people, in general, who are so poor (to some contextually-defined extent), cannot take care of their children as a rule; it is making a general observation, not referring to specific people who cannot take care of their children due to being poor.
It also has a very bookish sound; you are unlikely to encounter such a sentence in speech.

[Artashes98]

Good points, thanks.

[arthur473486]

When do i put o or ou in caeryain wourd, and how do i know if its talking him/her?

[VladaFu]

-ou is the typical verb ending for 3rd person plural - they. Those they can be any gender.