"Ich kümmere mich darum, dass...", "Ich rede darüber, dass..." – are 'darum' und 'darüber' redundant?

Question

Whenever I am using verbs that are complemented by prepositions like i.e. "sich um etw. kümmern" or "über etw reden" and I am about to introduce a subordinate clause, I never know if I should include those prepositions in the main clause as in:

Ich kümmere mich darum, dass sie nie hungrig sind.

or

Ich möchte darüber reden, was geschehen ist.

Are darum and darüber redundant? Would it be enough to say:

Ich kümmere mich, dass sie nie hungrig sind

Ich möchte reden, was geschehen ist.

I chose these two verbs purposefully as my gut feeling tells me that the first sentence does not require darum, whereas the second one sounds unnatural without darüber. Still, I have no idea why. Which is correct? Is there a rule that covers this subject?

Answer 1

Both your example sentences require to retain the preposition. If it's not required one time or another, you faced a free adverbial instead of a prepositional object.

Ich kümmere mich um acht Uhr darum.

See how the darum is still required?

Those hier- and da- variants of the prepositions are used for backreferences. You may see them as shortcuts for demonstrative expressions:

Ich kümmere mich um acht Uhr um dies hier.

Ich kümmere mich um acht Uhr um jenes da.

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English has a slightly different way to express the same thing but retains the preposition as German does:

Ich kümmere mich darum, dass sie nie hungrig sind.

I care about them never being hungry.

Ich möchte darüber reden, was geschehen ist.

I want to talk about what happened.