I did OB through Deakin in Melbourne. The course co ordinator is very helpful with advice. The course spans about a semester so you could def. do both peds and ob at the same time within a semester. It isn't anything very challenging, just time consuming. It's all online with an online exam and a few written assignments (a few case studies, a professional journal and a literary review from what I can remember). I was able to do it with a newborn baby!
A word of warning you have to organise the clinicals yourself ( I needed 2 weeks, so i'm assuming you would need approx 4 weeks but this varies from state to state how many hours you will need! ) which I found to be a huge pain. It was very very difficult to get in. I ended up finding a hospital that would have me but I ended up having to pay extra money on top of Deakin's fees to facilitate their clinical teacher. Deakin will not organise these for you!
All up it cost a few thousand dollars which is just for the OB. But if you are serious about working in the states then it's worth it. I have heard some rumors that certain states don't accept the course any more but I had no problems with CGFNS and Hawaii.
In terms of finding a job you should not have too much trouble the demand for RN's is always there depending on the area you live in.
Good Luck and let me know if you have any other questions. This whole process took me a few years so I know how frustrating and annoying it can be!