Radisson Blu
I had a great stay at the Hotel Berlin Berlin.
I can recommend the Holiday Inn Express Berlin City Centre. Though it's a little bit out of the way.
Start of my (otherwise 5 star) review on TripAdvisor "Berlin City Centre my backside! If relativity applies then, yes, it's closer to Berlin City Centre than my house. Just."
And their response "I'm happy that you like our rooms, our breakfast, our free wifi and our central location."
I've stayed in the Sofitel Kurfürstendamm several times and I'd recommend it. Nice hotel, reasonable rates and close to public transport.
I'd highly recommend doing a tour with Berlin Unterwelten. They're an association of historians who give tours of various bunkers around Berlin, many accessed through those big non descript brass doors you see in many U Bahn stations. We did two tours with them and they were fascinating.
If you or your son have any interest in cars, then a trip to Classic Remise is a must - http://remise.de/Classic-Remise-Berl...sh-summary.php