Hi! I'd love to help, as I've lived in the Dortmund area for over 8 years now, but no kids. Kindergartens abound here, but I've not heard of any specializing in English. Most teachers, however, will have rudimentary English, and deal often with children unable to speak German (mostly Russian, Polish, or Turkish). Used to be a lot of Brits stationed around here, though most have assimilated quite nicely. As for housing, depends on if you want to live in the city area, or on the outskirts. Also, certain area are very "multi-cultural", resulting in much more affordable rent, though not always the nicest or quietest of environments. The Nordstadt, Scharnhorst, and Hörde are a few of the afore mentioned areas. You can find quite nice places, warm, on the outskirts in the 400-700 Euro range, anywhere from 70-90 square meters.
www.immobilienscout24.de is a decent site to find a place, as well as www.immowelt.de. All depends on if you need to be close to the city self, and if you want to travel with public transportation or by car. Sorry I can't be more help, but if you have any other questions, I'd be happy to try and answer them.