Lehrplan 21 curriculum documents set out 'competences' for each subject area.
I found a web-page from Bern that lays out the competences in Lehrplan 21 against the European framework - minimum standard is B1 by the end of third cycle (end of SEK) for all areas.
Clearly, if a child is fluent in English at home, they should far exceed the minimum requirements for English as a second language.
In that case, I can highly recommend either asking if Cambridge exams are offered at SEK, or if you can do them privately. These will come in handy in the future. It depends if your kids are happy to do these as an extracurricular activity, and don't mind preparing for the exam.
However, a note:
- if your child is exempted from English the subject will be not counted in their grade average for SEK. If they can consistently get a 5-6 grade average for SEK English (anything less than 5 would be slacking off for English in our family and not acceptable) - this will bring UP their overall grade average - that can make the difference between staying in SEK A or moving to SEK B.
- your kids may actually 'enjoy' being an expert (for once!) in a subject, so keeping them in English class may be fun rather than boring (all my kids opted to do this as they actually enjoyed feeling like experts, did not mind teaching others as requested by the teacher, and felt heard and affirmed by their English teachers, who would then try to stimulate them further, or let them sit in the back of the class and do their other homework, extra German or French instead during 'English classes'.
None of my kids went for exemption for English at SEK - they were all given the option of doing Cambridge and getting an exemption, or staying in the English class - and they all chose to stay in the class.
Cambridge FIRST, ADVANCED or PROFICIENCY exceeds the Lehrplan 21 minimum standards, so if your kids pass these test (usually possible end of grade 6 or during SEK) then they would then be able to ask to be exempted from English as a subject at school. But as I said, that may not be an advantage to them in their overall school experiences.
My husband teaches in a bilingual Montessori school and the kids there who are English-fluent are able to take the Cambridge exam preparation process during grade 5 and sit the exam before the end of grade 6, but it's optional, based on the interest of the child, parents and the support of the teacher. They sit the the Cambridge FIRST for schools.