I have mounted kids seats on bents before, Rans Stratus and a Ryan Vanguard and a Rans Screamer. All of them were rear rack mounted seats. I'm not sure the Bobike could be used with a bent, but you never know until you try I guess.

I would suggest a trailer over any baby seat. A two wheeled trailer offers a much safer ride then any bike mounted seat. Not a cargo trailer but one made to haul children such as those offered by Burely and many others. Plus you get the added space for all the stuff that comes along with children.