I don't know what she has told you about schools so don' t want to just repeat it.
There is a Montessori bilingual kiga in Zehlendorf which might be nice for your youngest if you are planning on living SW (Dahlem, Zehlendorf, maybe Kleinmachnow, possibly even Babelsberg might be nice)
I suppose she told you about the JFK Am-German school whihc might not take you since you are not American and they tend to fill up year 1 so coming in late is tricky unless English speakers leave and they prefer to have American families. Then there is the Quentin Blake state Euopa-school bilingual in Engl and Gemran and located quite near that MOntessori Kindergarten.
There is a Phorms in Zehlendorf. I can't recommend it, no idea at all. Essentially it is a non particularly expensive private school German-English but they have no real established grounds, new set-up. Not sure about that.
Local schools in Dahlem/Zehlendorf should be ok if you want the purely German route. I agree though too short for your dc to learn enough GErman to participate really and they will not get much extra help.
Ther is also the Nelson Mandela State International school in Wilmersdorf which might work but it is a pain driving about town to get there at 8.
If you can wangle it , I'd recommend probably the JFK school, call directly the head of the American elementary school section. If you google JFKS Berlin, the school site would come up.