"Listen! Dad is talking in his sleep."
Translation:Lyssna! Pappa pratar i sömnen.
"pratar" instead of "talar", okay. But if you write "his sleep", then you should accept "sin sömn" ;)
Pratar i sömnen vs talar i sömnen, yes the latter is more common but both should be accepted. sin sömn should never be accepted.
Hmm... yeah, maybe you are right abouth the latter. Now that I say it out loud, it sounds a little strange with "sin". :)
Added that, it's an acceptable version. But actually both previous posters are mistaken. pratar i sömnen is much more common than talar i sömnen. A corpus search gives 16 hits for talar vs 227 for pratar.
talar is more formal so that expression may be a better fit for medical contexts. In everyday life, pratar is more idiomatic.
While I'm at it, cc08_ is right that i sin sömn sounds too strange. prata i sömnen is a fixed expression.