Rerunning children's programming generally requires fewer episodes than programming for adults. For most children's series, reruns are aired for a short period of time after the series finishes production, then are replaced. For weekly series, this practice dates to at least the 1960s, when Saturday morning cartoons would, after the end of their 13-week run, begin rerunning continuously for about a year (usually four runs/year) until being replaced by the next show, either new or archival. During the 1970s, 22 episodes was typically the number a producer sought in order for an animated program to be rerun beyond its first year. After several years, once the previous generation of children outgrew the show, it could be reintroduced for the next younger generation by airing reruns. For shows that are rerun daily, the time span is usually on the order of months. This also meant that cancellations of children's programming was extremely rare; because of the long lead time to produce a cartoon, networks usually bought a full season of a show before it began airing, meaning that it would be far too late to have any appreciable financial benefit by ending it.