we took our DD when she was 6 mo old. She went on almost everything with me. The exceptions were of course the obvious ones, and then we babyswapted and the other two kids loved that b/c they got to ride twice. I "wore" her in the front back 99% of the time and that's the way she went on the rides too. For the ones with the bars that come down, I'd just time it right and as they were coming down I'd lift her over the top of it and we were fine like that.
I'm trying to convince my sister to come down with us next year, but she's afraid of taking her then 8mo old. I told her out of all my kids, the baby was by far the easiest.