Ons strek sowel voor as na die pretdraf.

It is a paired conjunction meaning both ... and ....

So in Ons strek sowel voor as na die pretdraf, it links voor and na and emphasizes that both are true: we stretch before the fun run and after it.

Because the normal Afrikaans pattern is sowel X as Y.

If you use sowel, the matching word is as, not en.

• sowel voor as na = both before and after
• voor en na = before and after without the extra both emphasis

So Ons strek voor en na die pretdraf is also possible, but it is a slightly simpler version.

Strek is the verb, meaning stretch.

In Afrikaans, present-tense verbs usually do not change form depending on the subject:

• Ek strek
• Jy strek
• Ons strek
• Hulle strek

This is simpler than English, where you get forms like I stretch but he stretches.

This is a normal main clause in Afrikaans.

Afrikaans usually places the finite verb in the second position of a main clause. Since Ons comes first, strek comes second:

• Ons = first element
• strek = second element

Then the rest follows: sowel voor as na die pretdraf.

Yes.

The phrase means:

• voor die pretdraf
• na die pretdraf

Afrikaans often lets two linked words share the same complement, just like English does in before and after the fun run.

So die pretdraf is understood with both voor and na.

Here it functions as part of a prepositional time expression.

Even though die pretdraf appears only once at the end, it is understood with both words:

• voor die pretdraf
• na die pretdraf

So in this sentence, voor and na are best understood as prepositions expressing time relations.

Pretdraf is a compound noun:

• pret = fun
• draf = jog / trot / run

Afrikaans very often writes compound nouns as one word, so pretdraf is standard spelling.

English often uses separate words for the same idea, such as fun run.

Yes, absolutely.

That version is natural and means almost the same thing. The difference is mainly emphasis:

• Ons strek voor en na die pretdraf = plain statement
• Ons strek sowel voor as na die pretdraf = more explicit, with the sense of both before and after

So sowel ... as ... adds a bit of emphasis, and can sound slightly more formal or careful.