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.
However, parents of individual babies are in the best position to decide when their baby has the physical ability to ride in an umbrella stroller safely. Some infants may have no difficulty when they are as young as 4 months, while others may not be ready to sit up well until they are 7 or even 8 months old. If you are not sure whether your infant is developmentally ready for this type of stroller, then seek your paediatricians opinion.