Do you get your older baby a rear-facing car seat or a forward-facing one?
There are several threads in other areas of the site at the moment. Please have a look at the information from Rospa and the crash-test videos.
At the moment, rear-facing seats are stocked by only a small proportion of retailers in this country. In Scandinavia and parts of mainland Europe they are the norm. Hopefully in nine months time, when you're looking for stage 1 car seats, they'll be more readily available.
I wasn't aware of these for my first two children, but was lucky enough to find out in time for DC3. Enjoy your pregnancies :o