With the all-digital future arriving, if haltingly, and a bigger share of viewers likely to come through DTV multicast channels, public TV stations are reconsidering how to use their bitstream, making over their channels, and in some cases adding new services to woo audiences. The wee audience, for one. Little kids and their parents are a vital audience and constituency for public TV, and mockups of the stations’ future DTV menu often featured a dedicated channel for them. To supply it, stations had access to a 24-hour PBS Kids feed, packaged by PBS. That changed in 2005 when the network acceded to the desires of its two biggest producers for children and joined a partnership to package Sprout, a cable channel for preschoolers.