Questions regarding returning to the UK from the USA

I have been living in the USA since 2006 and have in that time got married in july 2006 had a son in March 2012 gained citizenship in January 2011 and also held down employment for most of that time. I currently have a job with a multinational software company that happens to have a London office. My question is simple - if my company would be happy to transfer me to London, how difficult would it be to bring my family to live with me permanently. Is my son a UK citizen by default because I am british? What would my wife have to do? she is US born.

Hopefully someone can shed some light on this for me.

Your wife will have to apply for a spouse visa.  You will have to meet financial, accommodation and relationship requirements.  The financial is usually the most tricky.  You, the UK citizen will have to have had a job making at least £18,600/year while in the US and you will have to have a guaranteed job starting within 3 months of your return to the UK making the same amount or more.  You'll also have to have adequate accommodation lined up before you move.

Your son should be a UK citizen so all you will need to do if apply for a UK passport for him. 

Read through the spouse visa info on the UKBA website:

http://www.ukba.homeoffice.gov.uk/visas-immigration/partners-families/citizens-settled/spouse-cp/apply-outside-uk/