The south of the UK, are the "modeling" must see places?

There are some excellent places in the south, but it depends on how far you want to travel (totally biased towards aircraft);

Imperial War Museum (London, 75 miles)

http://www.iwm.org.uk/visits/iwm-london

RAF Hendon (85 miles);

http://www.rafmuseum.org.uk/

Brooklands (90 miles);

http://www.brooklandsmuseum.com/

Duxford (110 miles North);

http://www.iwm.org.uk/visits/iwm-duxford

Tangmere (120 miles);

http://www.tangmere-museum.org.uk/

The Fleet Air Arm Museum (190 miles East);

http://www.fleetairarm.com/

The Tank Museum in Bovington (190 Miles East);

http://www.tankmuseum.org/

Have a look at this link, it list museums & POI in distance bands;

http://www.distance-calculator.co.uk/museum-near-dover-great%20britain.htm

Dover Castle of Course! Enough there for 2 days at least!

Info here: www.english-heritage.org.uk/.../dover-castle

2 Henry 8th forts right up to WW2 tunnels & lots of artillery....

You don't say where you are from, but foreign visitors can get 9 or 16 day passes,  

www.english-heritage.org.uk/.../prices-and-how-to-order

UK residents can get annual passes, & you can take a whole herd of kids for free on the adult pass.

London IWM, & Hendon are good, Duxford & Bovington are worth a trip if you have the time.

I am from the Netherlands so I will have to look into that foreign visitors pass.

Thanks for all the suggestions. I am traveling with my wife and my one year old son. So I will not be traveling huge distances. Or visiting a museum for the whole day. But my wife is very supportive of my hobby so if anything is in the neighbourhood (or can be combined with a family activity) she is okay with it.