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, airing on weekdays (during the morning or afternoon hours) and Sunday mornings. Attempts to reach a time-lease agreement deal with Disney were called off one week after negotiations started due to a dispute between Disney and UPN over how the block would be branded and the amount of E/I programming that Disney would provide for the block; UPN then entered into discussions with then-corporate sister Nickelodeon (both networks were owned by Viacom) to produce the new block. That February, UPN entered into an agreement with Saban Entertainment (then a subsidiary of Fox Family Worldwide, owned jointly by Fox, which Disney later acquired in 2019, and founder, Haim Saban, who also owned competing block Fox Kids) – which distributed two series recently aired on the UPN Kids block around that time, Sweet Valley High and Breaker High – to program the Sunday-to-Friday 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 on weekdays (from 7:00am – 9:00am or 3:00pm – 5:00pm) and Sunday (from 9:00am – 11:00am). 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 (incidentally, "whomp" was used as a pejorative term in the Disney-produced animated series Recess, one of the series that would end up part of the new block, as a substitute for "sucks").
The new lineup was later renamed Disney's One Too in July 1999, formatted to serve as a competitor block to ABC's existing children's block Disney's One Saturday Morning. The block debuted on September 6, 1999, replacing UPN Kids, which ended its run the day before (on September 5) after four years. Compared to the format of One Saturday Morning, One Too varied in that, instead of incorporating hosted segments, short gag segments from the shows featured in the block (such as Sabrina: The Animated Series, Doug and Recess, all of which – along with a few other series – were originally aired on One Saturday Morning) were usually shown, often preceding the start of each program, and after commercial breaks. The block also featured a different opening sequence, using more futuristic buildings and a theme similar to that used on One Saturday Morning. Many shows previously aired on One Too continued in reruns on Toon Disney and Disney Channel.
In September 2002, the One Too branding was discontinued as a result of the rebranding of the ABC block from One Saturday Morning to ABC Kids; although the UPN block was not revived, the Disney.com website referred to it under the title Disney's Animation Weekdays. The block aired for the final time on August 31, 2003, with the block being replaced with the new UPN Kids revival block the following day.
In 2015, ABC decided to expend children's programming to seven days a week, which led to the re-launch of Disney's One Too on the network, making it the very first time that ABC aired children's programs seven days a week, unlike most networks where they'll only air such programming six days a week. Since then, ABC became the new place for all One Saturday Morning shows every day of the week.
- Buzz Lightyear of Star Command (2000-03)
- Doug (1999-2001)
- Hercules (1999-2000)
- The Legend of Tarzan (2001-03)
- Pepper Ann (2000-01)
- Recess (1999-2003)
- Sabrina: The Animated Series (1999-2002)
- The Weekenders (2001-02)
- Phineas and Ferb (2015-2017)
- Milo Murphy's Law (2017-Present)
- Vampirina (2017-Present)
- Star Vs. The Forces of Evil (2016-2020)
- Fancy Nancy (2020-Present)
- Penn Zero: Part-Time Hero (2015-2018)
- DuckTales (2017 TV Series) (2018-Present)
- The Rocketeer (2019 TV Series) (2020-Present)
- The Owl House (2020-Present)