Well, you're not going to be going at huge speeds so coming off the seat forwards should not worry you too much, nor should the geometry. Tourer / town bike style for preference.
I agree entirely about the poor balance of rear child seats. I've had the bike tip under me when I've been stationary. Go for a top-tube mount.You'll be able to talk to them better, and their view will be improved as well.
Unitl it got nicked, I had a (Specialised) hybrid with rack-mounts half-way down the forks. I fitted a tri-cross bar extension so the kids could lean forward, and instead of having footrests on the down tube, I fitted aluminuim extrusions onto the fork rack mounts. (square section, last few cm flattened, bent, drilled, bolted on. Very easy. They never hit their legs on the tyres.
I also cut the wire back-rest off the top-tube child seat so I could get on/off more easily