Sounds like a bit of a dilemma!
How relatively secure are the two jobs? There are indications we're going into a serious recession (the problems of 2008 were temporarily put off but not solved while other factors have worsened) but world governments' responses are generally just to print more money, further devaluing currencies and our spending power. If either of the jobs is more secure and/or more likely to stay do well, or keep going, in hard economic times then I would suggest it could be a safer option.
Few possible ideas:
If you did stay in your current job is it possible to rent somewhere closer to your work at all for a similar or lesser price? If you lived close enough to your workplace to walk or cycle in you could cut down a lot on car use and be less effected by future spikes in petrol prices, which are expected to go up a lot over the coming years.
Is it possible for your wife to do a little bit of child-minding perhaps? Like taking on one or a few other children to look after as well as your son at time? Just on a informal basis with friends or other mothers she knows.
I guess you've probably already tried cutting down spending on luxury food, getting the cheapest utilities, etc?
http://www.moneysavingexpert.com/ is a good place for that sort of thing.
If you've got a garden at all try growing some food to save a bit of money?
Good luck!
