These are my thoughts on it:

The extra money will be great! And it may make up for the fact that you will not get paid maternity leave. What are the chances like of them making you permanent? If the chances of them making you permanent are very good or guaranteed, then I'd go for it. That is, if you think you'd like to do the job and dont mind the travelling time. The work from home thing sounds great too, and the flexible hours would be excellent for you. Like Chloe though, I get bored and frustrated with jobs that I can do with my eyes closed, so that would also be an issue for me.

Having worked in those labour hire jobs on 12 month contracts before, it can be pretty sucky when your contract is coming to an end and they dont wish to renew it. That has happpened to me before whilst working at a relatively large organisation in 2004/2005. There were about 7 of us whos contracts werent renewed and it was for no good reason at all and with very little notice too. I absolutely hate not hving a permanent job. Its too easy for them to get rid of you.
When would you start at this job? and would there be any chance of them offering you another 12 months at the end of the first 12 months if you havent gone on mat leave by then? Its a bit of a blow if they decide not to renew your contract/make you permanent, and if it happens to be at the beginning of your pregnancy are you going to want to go through the hassle of applying for new jobs elsewhere or are you going to sty off work for the rest of your pregnancy? Will you NEED to get a new job very soon if they decide not to renew your contract? Or can you cruise around jobless for a while?
Also, do you think you'll want to go back to work after having this next bubba?
Will the fact that your job is not permanent affect the home loan?? I know I had big issues with the fact I was in labour hire and my mortgage lender didnt want to lend the money to us, just because I wasnt permanent.

ok sorry I wffled on so much, but I was just writing down all of the things I would consider if I was in your situation! Good luck and hope you can make the right choice for you and your family.