To the OP: we have recently made the transatlantic move twice in one year US-UK-US (without pets or kids). The things you should think about before moving to the US are:
1) Getting green card for spouse could take up to a year. It took us 9 months w no restrictions, though again that was over 5 years ago. I would expect a minimum of 6 months. Check
http://london.usembassy.gov for details of where to start.
2) You should definitely get your UK naturalisation. I am kicking myself for not having done so before moving back. We were so concerned with getting his GC we just didn't even research it until it was too late.
3) Will you sell or rent out your house - and will you require the proceeds to move / help with the financial sponsorship requirements? Could this affect your desired timeline?
4) The job market sucks. Both in the UK and in the US. I would definitely recommend getting a job first, if either of you can. If not, when you are back in January visiting family, maybe you can do some hard core research then. Meet with recruiters or contacts in your industries. My spouse gets hired from Skype interviews, so when his project came to an end abruptly in London, within 2 weeks he was already offered and accepted a contract back in Los Angeles. On the flip side, I just started a 3 week freelance job - my longest gig since we moved to the UK a year ago. I suppose what I am saying is that if it were me and my spouse, I would not move anywhere without having a secure job for one of us first.
5) Shipping companies. We used a US broker - Southern Winds. We shipped 200 cubic feet (shared container - 1br flat of stuff) from London to Los Angeles and it cost us USD$2600 or thereabouts including packing, removal and insurance ($10k worth). We ended up using that insurance so don't skimp on it! Shipping took 10 weeks for us. Short term accommodation is a potentially expensive bank account buster, the average furnished apartment here being about $3600/mo. We ended up renting a room from a friend for much cheaper.
6) Health care costs. Need I say more
I'm not saying don't go for it -- if this is what you both want for your family, then definitely pursue your dream! And it's good that you are researching this from all angles. If you have any questions, maybe hitting britishexpats.com can help further. DH used this when we moved back the first time. Best of luck!