Are there indefinite and definite articles? I wrote "Mara and a child" and it was accepted
Child isn't countable though, is it? Child is strictly singular. The -ren suffix is added when more than one child is being discussed.
I can accept that "Mara and child" may be awkward, but it should be technically correct, no? The phrase "mother and child" is used without confusion.
The word "child" is a countable noun because it is possible for form a plural (children).
"furniture" is an example of an uncountable noun because we can't talk about "furnitures".
Whether to accept things that are awkward and may or may not be technically correct is something we may have to discuss a bit more in the team; for now, I'd recommend translating into non-awkward English and then you can avoid the question of whether something is only technically correct.
"Mara and child" strongly implies that the child is Mara's son or daughter, as it does in "mother and child". Since we don't have that much information, it's best to use some kind of article here.