"They have children."
Translation:One mają dzieci.
no, if at leas one male is in the group - use oni. it can be 1 man and 10 women - oni
Question: if you did not need to specify which type of "they" you mean (I can't currently think of an example...maybe if you didn't know the genders of those in the group?), would you be able to merely say "Mają dzieci."? Or is it a rule that you have to specify whether the group contains a male or not?
3rd person pronouns are the ones that are less often omitted, but they still can. Either because of what you said, or just because "they" were just mentioned in the previous sentence so we know perfectly well who they are.