3,952,841 babies born annually in the United States.. I don't know how long you need toddler seat, maybe 3 years?

so, 12M families would like to own a car for 3 years.. (approx. multiple with number of children)

Most kids need some sort of seat until they are 8-10.

http://www.cdc.gov/motorvehiclesafety/images/child_passenger...