Article usage: (a/the) mother and child

Question

I am intrigued by these three sentences in dictionaries:

1. Mother and child form a close attachment.
2. Physical contact between a mother and child is very important.
3. Mother and son lost contact when Nicholas was in his early twenties. 

Do the following rewrites sound good? Is there any difference?

4. A mother and child form a close attachment. 
5. Physical contact between mother and child is very important.
6. The mother and son lost contact when Nicholas was in his early twenties. 
7. The mother and the son lost contact when Nicholas was in his early twenties. 

I guess sentence 5 does not work, because physical contact forces us to create the image of two subjects.

A dictionary says that “a” is used once before two nouns that are mentioned together very often, for example, “I'll fetch you a cup and saucer. Does everyone have a knife and fork?” Therefore, I guess it is not good to write “a mother and a child” in sentence 1 and 2.

Answer 1

A mother and child form a close attachment.

Mother and child form a close attachment.

Physical contact between a mother and child is very important.

Physical contact between mother and child is very important.

To me, these two pairs of sentences convey the same meaning.

In each pair, the top one denotes one specific pair of mother-child, while the second one denotes pairs of mother-childs in general.

The mother and son lost contact when Nicholas was in his early twenties.

The mother and the son lost contact when Nicholas was in his early twenties.

To me, the sentence below is more grammatical, as The mother and son feels like a noun phrase; as such, the above sentence has no object (with whom have they lost contact?). Meanwhile, the object of the sentence below is automatically conveyed as both the mother and the son, since lost contact with changes to a reciprocal verb (a verb that affects both parties involved [A → B; B → A]) when and is present.

Unfortunately, I have no other sources other than my ears. However, I do hope this helped!

_{Edit: I recommend that you don't dwell too much on articles. Unlike other Indo-European languages, the importance of articles in English is miniscule.}