frange(), a range function with float increments (Python recipe) by Dinu Gherman ActiveState Code (http://code.activestate.com/recipes/66472/) Sadly missing in the Python standard library, this function allows to use ranges, just as the built-in function range(), but with float arguments. All thoretic restrictions apply, but in practice this is more useful than in theory.
When I worked at a daycare we would have bike day during the summer when kids, aged 3-5, could bring in their bikes and ride them, most of the kids were on big bikes with training wheels and a few of the 4-5 year olds were without training wheels.
Summary: Babies must be at least one year old before you try them in a bike trailer or seat. This page highlights what we believe to be the risks of taking your baby along. It discusses advantages of baby seats and trailers. There is an opposing view at the bottom.