In January 1998, UPN began discussions with The Walt Disney Company (owner of rival network ABC) to have the company program a daily two-hour children's block for the network but attempts to reach a time-lease agreement deal with Disney were called off one week later due to a dispute between Disney and UPN over how the block would be branded; UPN then entered into discussions with then-corporate sister Nickelodeon (both were owned by Viacom). In February 1998, UPN entered into an agreement with Saban Entertainment – which distributed two series already seen on the UPN Kids block around that time: Sweet Valley High and Breaker High – to program the Sunday through Friday morning block.
In March 1998, UPN resumed discussions with Disney and the following month, The Walt Disney Company and UPN came to an agreement to provide Disney-produced programs on the network every Sunday (from 8-10 a.m.) and Monday to Friday (from 3-5 p.m.) The block was originally announced under the working title "Whomptastic", though the name was changed prior to the debut of the block for greater brand identity. The new lineup, which was created as a sister block to Disney's One Saturday Morning on ABC, was called Disney's One Too. Programming would included shows from One Saturday Morning like Disney's Recess, Disney's Doug, Disney's Pepper Ann and Disney's Hercules. Also, the Disney Afternoon shows on One Two would be sponsor as on Afternoon by Kellogg's.
The block debuted on September 5, 1999 on UPN, seventeen months after Toon Disney was launched. Compared to the format of One Saturday Morning, One Too differed in that, instead of hosting segments, short gag segments from the shows featured in the block (such as Sabrina: The Animated Series, Doug and Recess) were usually shown, often proceeding the program before it began, and after a commercial break. The block also featured a different opening sequence, using more futuristic buildings and a theme similar to the one used on One Saturday Morning. Many shows formerly featured on Disney's One Too continued in reruns on Toon Disney and Disney Channel.
Due to the rebranding of the ABC block from One Saturday Morning to ABC Kids, the One Too branding had been dropped for the block's final season on the air, leaving it unbranded, though the Disney.com website referred to the block as Disney's Animation Weekdays. The block last aired on August 29, 2003, leaving UPN as the only "big six" broadcast television network without children's programming, and one of only two major commercial broadcast networks that did not air a children's programming block (the other being Pax TV, which discontinued its Pax Kids lineup in 2000, before reviving children's programming as Ion Television through the 2007 launch of Qubo).
UPN was not the first "big six" network to drop children's programming: NBC became the first to drop kids shows entirely in 1992, when the network launched a live-action block for teenagers called TNBC (however, children's programming returned to NBC in 2002, through a time-lease agreement with Discovery Kids). To date, ABC (which dropped the ABC Kids block entirely in 2011, when it was replaced by a live-action family-oriented E/I block called Litton's Weekend Adventure), CBS (which dropped the Cookie Jar TV block entirely in 2013, when it was replaced by a live-action family-oriented E/I block called CBS Dream Team), Fox (which dropped its 4Kids TV block on December 27, 2008) and MyNetworkTV (which has never ran children's programming since it launched in 2006) are the only television networks that do not air children's programming or whose E/I program content is not strictly aimed at children.
In most markets, UPN affiliates used the network's recommended scheduling for the block (3:00 p.m. to 5:00 p.m. on weekdays and 8:00 a.m. to 10:00 a.m. on Sundays) – though some stations (such as New York City's WWOR-TV, Los Angeles's KCOP-TV and Denver's KTVD-TV) aired the weekday block in the morning-only hours, running from 7:00 a.m. to 9:00 a.m.