I think it should allow "The child is playing with their cup" as a gender-neutral alternative to "its". Since its is seen as a bit dehumanising and they and their are accepted as a gender neutral alternative to he/she and his/her, respectively.
(Yes, this does introduce singular/plural uncertainty into English which does not exist in German, but that doesn't make it wrong.)
You're right. I didn't realize it until later that Kind was going to be referred as "its" no matter what, kind of like Mark Twain's joke about "Mädchen."
Gretchen: "Wilhelm, where is the turnip?" Wilhelm: "She has gone to the kitchen." Gretchen: "Where is the accomplished and beautiful English maiden?" Wilhelm: "It has gone to the opera."
Whether you use "its" or only "his" or "her" when referring to a small child depends on where you come from in the English speaking world, I think. "Its" is used in Australia when you aren't concerned with specifying gender. If I heard someone say "The child is playing with his cup." out of context I would probably think that the cup belonged to another man or boy, not necessarily the child.
With 'Tasse' being masculine and in dative form, why is it 'seineR Tasse' and not 'seineM Tasse'?
I stand corrected. Makes more sense now. Thank you, I really thought Tasse was masculine.
If you are still curious, the genitive form of "es" is "seiner", which is used to designate possession in a way. In spoken German, I have been told that this case doesn't exist as it is usually replaced by "von(may change) + (dative here)", so in this case, "an ihm" if it was spoken.
To help remember this, think of it as "of (base word)".
So the phrase "Wir gedachten seiner." (We thought of him) can also be...
Wir dachten an ihn. (We thought of him)
Either way is correct, really. Still, in spoken German, the genitive form just isn't used according to a grammar site. "von" or "in" or "an", or whatever is used.
It is not really an acceptable thing to call a child socially in English. As previously stated it should be the child is playing with their cup. No civilized English person would call a child it as it can cause severe psychological harm to the child. I do not know about the rest of Britain though as i lived in southwest Scotland for a time during my childhood and their culture meant that they didn't count or treat children as people which caused me to have multiple suicide attempts and a nervous breakdown.