I did a lot of internet research a few years ago when I couldn't find a bike helmet to fit my 1 year old. Boy was I amazed at the info out there. 1)they don't make helmets that small because a child under that age is not suppose to be on a bike(front or rear seats).....I had no idea. Some reasons the sites gave were that their heads and necks were not yet strong enough for the jostle of a bike ride. The sites were VERY opposed to the seats that attach in front of you because if you crash, you fall on your child. I have the seat in front of me now that my child is older, but mainly because she was too fidgety when she was in the seat behind me and I couldn't see what she was doing. The web sites were also totally against the bike trailer for kids under age 2 because they are so bumpy. The one site even said, "you(the adult) get in the trailer and see how it feels to be wildly bounced around".
These were just some things I hadn't thought about. And although a lot of these web sites are a little on the extreme side, it at least gets you thinking more about safety. We live close to a bike trail, so we would go to the park and my hubby would put the kids in the wagon or stroller while I rode along on my bike, until the kids were old enough to do the trailer and the front seat rider.