Why was the sentence about being a father of three translated as "jsem otec trech detich" (IIRC) but being a mother of three uses a different declination?
Now you can use both forms, according to the new spelling rules. (Does not matter if it is a father or a mother of three children). TŘÍ / TŘECH is the same, both is OK, but Třech is better to use in spoken Czech only. Here in DUO they probably want to show you both forms. A couple years ago it was only possible to use the form TŘÍ.
Understood, thank you, I think I confused myself thinking it was also a different ending to "deti" but that's my fault
Consistent with the acceptable translations on the "father of" exercise, alternatives using "the" have been added.
It looks grammatically correct but sounds strange to me. Probably because you're not talking about any specific 3 children, so there's no point to emphasise that you are the mother. But "I'm the mother of THESE three children." is perfect, and in that case you can't use "a" instead of "the" (except if the children have more than one mother).
I hope this makes sense :)
It actually IS grammatically correct, and it sounds perfectly normal to me (native US English speaker).
A few minutes ago, "THE father of XXX children" was accepted in another exercise. So I've reported this one, in case DL wants to accept "the" here, too... or maybe to "un-accept" it in the other exercise. :-)
It's true, though, that there was no "the" equivalent in either Czech sentence, which might make both answers with "the" instead of "a" incorrect.
I just got marked wrong for typing "the mother" instead of "a mother" on one of these, even though the former is by far the more common way of saying that to me (native UK English speaker). I'd be more comfortable with "a mother to X children", but if it's "of X children" then I'd say "the mother" every time.