Learn Hardcore Swedish: Vi övar tillsammans när barnen sover. - We practice together when the children are sleeping.

Main clause (Vi övar tillsammans): Swedish is a V2 language, so the finite verb (övar) sits in second position. With the subject first, this gives Subject–Verb–(rest).
Subordinate clause introduced by när (när barnen sover): there is no V2. The normal order is Subject–Verb, so it’s barnen sover, not “sover barnen.”

Why is there no comma before “när” here?

Swedish typically does not use a comma before a subordinate clause that follows the main clause. So Vi övar tillsammans när barnen sover is standard. If you put the när-clause first, you normally add a comma after it: När barnen sover, övar vi tillsammans.

Can I put the time clause first?

Yes: När barnen sover, övar vi tillsammans.

Because Swedish is V2, when the subordinate clause comes first, the finite verb of the main clause (övar) must still be in the second position of the main clause: “(När barnen sover), övar vi …”

Does Swedish present tense “sover” mean “are sleeping”? Can it also refer to the future here?

Yes. Swedish present covers both English simple and progressive: barnen sover = “the children sleep/are sleeping.” In time clauses with när, Swedish often uses present even for the future:

Vi ska öva i kväll när barnen sover. = “We’ll practice tonight when the kids are asleep.”

Should I use “när” or “medan” here?

Both can work, but they differ slightly:

när = “when” (point in time or general time) and is very common: Vi övar … när barnen sover.
medan = “while/during the time that,” emphasizing simultaneity: Vi övar … medan barnen sover. You can use medan to stress that the two actions overlap in time. Use när more generally (and not with the meaning “while” in contrastive clauses).

Can I use “om” instead of “när”?

Not if you mean “when.” om means “if.”

Vi övar … om barnen sover = “We practice … if the kids sleep,” which is conditional.
Vi övar … när barnen sover = “We practice … when the kids are sleeping.”

What’s the difference between “öva,” “träna,” and “repetera”?

öva = practice a skill, rehearse; very common for music, language, performance, etc.
träna = train/work out; also used for practicing skills, but leans more toward training or drills.
repetera = rehearse (e.g., a play/concert); also “to review” material.
In your sentence, övar is the most neutral choice.

Where can I put “tillsammans”? Is “Vi tillsammans övar …” okay?

Natural placements:

Neutral: Vi övar tillsammans …
Fronted for emphasis: Tillsammans övar vi … Avoid: “Vi tillsammans övar …” (sounds odd). If you add who you are together with, use tillsammans med: “Vi övar tillsammans med kören.”

Do I need “med” after “tillsammans”?

Only if you specify with whom:

Without object: Vi övar tillsammans. (we practice together)
With someone: Vi övar tillsammans med barnvakten. (together with the babysitter)

How do I negate this? Where does “inte” go?

In the main clause, place inte after the finite verb: Vi övar inte tillsammans när barnen sover.
In the när-clause (a subordinate clause), sentence adverbs like inte go before the verb: … när barnen inte sover.
Note the meaning difference:
Vi övar inte tillsammans när barnen sover. = We do not practice together at that time.
Vi övar tillsammans när barnen inte sover. = We practice together when the kids are not sleeping.

What if I want to say “when the kids have fallen asleep,” not just “are sleeping”?

Use perfect tense to mark the completed event:

Vi börjar öva när barnen har somnat. = “We start practicing when the kids have fallen asleep.” This focuses on the moment they fall asleep, not the ongoing state.

How does “barnen” work grammatically?

barn is a neuter noun with the same form in singular and plural:

ett barn = a child
barnet = the child
barn = children (indefinite plural)
barnen = the children (definite plural) Possessive plural: barnens (“the children’s”). Don’t say “barnarna.”

Any quick pronunciation tips for this sentence?

övar: the ö is a rounded vowel (like German “ö”; think of “e” in “bed” but with rounded lips). The a is short.
när: long ä (like a long “eh” sound).
barnen: long a (like “ah” in “father”); in much of Sweden, rn merges to a retroflex sound.
tillsammans: stress on “-sam-”; double mm is a long consonant; final -s is pronounced.

Why isn’t there “att” before “övar/sover”?

att is the infinitive marker. Here, övar and sover are finite present-tense verbs, so no att.
Use att with an infinitive: Vi övar på att sjunga.

How do I say what we’re practicing?

Several patterns are natural:

Direct object: Vi övar svenska tillsammans …
“på att” + infinitive (very common): Vi övar på att prata svenska …
With träna: Vi tränar på att uttala ö-ljudet …

How do I say this in the past or future?

Past: Vi övade tillsammans när barnen sov.
Future: Vi ska (eller kommer att) öva tillsammans när barnen sover.
Note that in the när-clause you still often use present (sover) even for future time.

Is “ligger och sover” or “håller på att sova” better than just “sover”?

ligger och sover is idiomatic if you want to paint a picture of someone lying down sleeping.
håller på att sova is unusual; Swedish normally just uses sover for “is sleeping.”
In most contexts, plain sover is the natural choice.

Are there common learner mistakes with these words?

Spelling: write tillsammans (two m’s), not “tillsamans.”
Don’t invert in the när-clause: say när barnen sover, not “när sover barnen” (that would be a question).
Don’t add är before sover: not “barnen är sover.” Just barnen sover.
Don’t use om for “when” unless you mean “if.”