Min søn glemmer altid svømmebrillerne, når vi tager til stranden.

In Danish, a possessive like min already does the job of an article, so you normally do not add another article before the noun.

• min søn = my son
• not den min søn

This works like:

• min bil = my car
• vores hus = our house

So min søn is the normal and correct form.

Glemmer is the present tense of at glemme = to forget.

Danish often uses the present tense for things that happen regularly or habitually, just like English does:

• Han glemmer altid... = He always forgets...
• Vi tager til stranden om sommeren. = We go to the beach in summer.

Here, the sentence describes a repeated habit, so present tense is the natural choice.

In a normal Danish main clause, the finite verb usually comes early, and adverbs like altid often come after it.

So:

• Min søn glemmer altid svømmebrillerne

This is the natural order:

• subject: Min søn
• verb: glemmer
• adverb: altid
• object: svømmebrillerne

That is very typical Danish word order.

Svømmebrillerne is a compound noun made from:

• svømme = swim / swimming
• briller = glasses / goggles

So svømmebriller means swimming goggles.

Then -ne is added to make it definite plural:

• svømmebriller = swimming goggles
• svømmebrillerne = the swimming goggles

Danish uses compound nouns very freely, so this kind of word is extremely common.

Because the sentence refers to a specific pair of swimming goggles that both speaker and listener can identify from the situation.

So:

• svømmebriller = swimming goggles, in general
• svømmebrillerne = the swimming goggles / the goggles

In natural English, you might often just say my son always forgets his goggles, but in Danish it is very normal to use the definite form when the object is understood from context.

Yes, you could say Min søn glemmer altid sine svømmebriller.

That would mean more explicitly:

• his own swimming goggles

The difference is roughly:

• svømmebrillerne = the swimming goggles, the ones we mean in this situation
• sine svømmebriller = his own swimming goggles

Both can be natural, but svømmebrillerne sounds very idiomatic when the goggles are already understood from context.

Yes, very much so. Briller is normally used in the plural, just like English glasses. The same applies to svømmebriller.

So you usually say:

• briller = glasses
• svømmebriller = swimming goggles

Even when talking about one pair, Danish still normally uses the plural form.

Når is used for when in the sense of something that happens repeatedly, regularly, or generally.

Here the meaning is habitual:

• Every time we go to the beach, my son forgets the goggles.

So når is the right choice.

A useful contrast:

• når = when, whenever, in repeated/general situations
• da = when, for one specific event in the past

So this sentence needs når, not da.

Because når vi tager til stranden is a subordinate clause, and subordinate clauses in Danish do not use normal main-clause inversion.

So you get:

• når vi tager til stranden

not

• når tager vi til stranden

A simple way to remember it:

• main clause: Danish often has verb-second order
• subordinate clause: the subject usually stays before the verb

Here tage til is an idiomatic expression meaning go to or head to a place.

So:

• vi tager til stranden = we go to the beach

It does not literally mean take to the beach in English. This is just how Danish often expresses movement to a destination.

You may also hear other verbs depending on context, such as går til stranden if people are walking there, but tager til stranden is a very natural general way to say go to the beach.

Because til shows movement toward a destination, while på usually shows location.

Compare:

• Vi tager til stranden. = We go to the beach.
• Vi er på stranden. = We are at the beach / on the beach.

So:

• til = to
• på = at/on

This is a very common Danish distinction.

Stranden is the definite form:

• en strand = a beach
• stranden = the beach

Danish often uses the definite form for familiar destinations, especially when the place is understood in context.

So til stranden is very natural for to the beach.

It is common, but this depends on the comma system being used.

In Danish, a subordinate clause introduced by når may be preceded by a comma if the writer uses startkomma. Many modern writers omit that comma under the newer system.

So both of these may be seen:

• Min søn glemmer altid svømmebrillerne, når vi tager til stranden.
• Min søn glemmer altid svømmebrillerne når vi tager til stranden.

The version with the comma is very common and fully correct in the traditional system.

Then the main clause must still follow Danish verb-second order.

So:

• Når vi tager til stranden, glemmer min søn altid svømmebrillerne.

Notice that after the fronted clause, the verb glemmer comes before the subject min søn.

This is a very important Danish pattern:

• fronted element + finite verb + subject

So you do not say:

• Når vi tager til stranden, min søn glemmer altid svømmebrillerne

The correct version is:

• Når vi tager til stranden, glemmer min søn altid svømmebrillerne.