Before 1993, children's programming on PBS used the adult-oriented idents, up to the Orange CGI P-Heads.
On September 6, 1999, in addition to the new generation of PBS Kids premiering on PBS stations across the United States, the Public Broadcasting Service itself launched PBS Kids as its own digital broadcast television network as well. This network, like all other over-the-air networks, broadcasts programs in different orders, depending on whichever U.S. state the station is located.
This was the first PBS Kids ident, starring the P-Pals. It appeared on Mr. Rogers' Neighborhood, Sesame Street, Shining Time Station, Square One TV Math Talk, Reading Rainbow, Where in the World is Carmen Sandiego, Barney & Friends, Lamb Chop's Play-Along, Bill Nye the Science Guy, Kino's Storytime, The Magic School Bus, The Puzzle Place, Wishbone, etc.
Following that are two more variants, the short version which features PTV Park, and another without the "PBS" text and the animation goes "Surprise!".
Finally, in late 1996, starting with Mr. Conductor's Thomas Tales, the P-Pals ident now included an additional E/I balloon. This appeared on Arthur, seasons 4-5 of Barney & Friends, season 2 of Wishbone, Where in Time is Carmen Sandiego, Teletubbies, season 1 of ZOOM, etc.
You'll still find this logo on VHS prints of PBS Kids shows from the 1990s decade. Although the logo was no longer seen by many PBS Kids fans by the early 2000s, it was rediscovered on YouTube in August 2006, along with the other variants later in 2006.
Up until 2009, this logo was seen on all children's programming from 1999 to 2009, ever since PBS Kids launched as a digital terrestrial television network in many PBS stations across the United States since September 6, 1999. It often plasters the P-Pals ident. Though no longer current, it can still be seen on reruns of some older PBS Kids programs.
For shows that are part of other blocks, they used the blocks' PBS Kids ident instead. For example, Wishbone used the PBS Kids GO! ident from 2007 (the block began in 2004 with older idents).
Today, the PBS Kids ident is shown in many different variants, just like the 9th PBS ident from September 2009.