Just thought I'd follow up here with some feedback about child seats now that it's nearly 18 months later.
I bought a Bell child seat that mounts on the back, and she rides in that and loves it. I have the iBert on the front of my cruiser, and she loves that, too. The only problem with the iBert is that it sits far enough back that I can't get between it and the nose of my seat, so I can't straddle the tandem to let my wife on and off in the back. So the rear seat ended up being the way to go for a couple reasons.
Another issue with the iBert is that you can't stand at all. I have one hill to get to my house, and it would be awesome if I didn't have to grind my cruiser up sitting down. Add to that the fact that the combination of the arched top tube and short stem height meant there was really not enough room for the seat, the top tube, my daughters legs and the handlebars to fit all in the right place, I ended up making a mount for the seat that put it above the bars and moved it forward. It's harder to get her in the seat (it's a bit tippier) but it's easier to ride, because the weight is balanced better.
I'm going to move this mount to the tandem, and then make another one to mount a little bit further forward, so I can stand up and pedal a bit better. I really think iBert should make an optional bar-top mount. It really does ride nice.
More thoughts: My daughter does fall asleep in the rear seat, and crashes against my wife's back. But she has never fallen asleep on the front seat. So it doesn't appear to have been an issue.
Generally, I think she prefers the iBert. I know I prefer it. I really like having her in front of me, where I can see what she's looking at, point out birds, dogs, trucks, and airplanes.
That's with the factory mount. You can see how her legs have to go under the bar, and there's inadequate clearance between the seat and the top tube.
The other cool thing about the iBert is that you don't get this kind of interaction when your kid is in back:
And a last thought about age: My pediatrician had cleared us at 6 months to take her out with the helmet. However, because of bike seat fitment, we didn't do it until 13 months or so. In retrospect, that was a good thing. I see how much her head bobs in the bumps now, I would have worried too much with her at 6 months. The next kid, in the car seat in the bakfiets, however....