The two-year, six-figure deal will see TMi create a campaign for Aquafresh brands Milk Teeth, Little Teeth and Big Teeth.
The campaign will be aired across digital and terrestrial channels in the UK.
The 90-second spot will go live on 19 November, playing exclusively at 7pm nightly on Turner Broadcasting's pre-school channel Cartoonito.
The ad uses 3-D animation to bring to life the red, white and blue Aquafresh colours in the form of three "nurdles" - the name used to describe a squirt of toothpaste.
The trio, called Billy, Lilly and Milky, each represent the age groups targeted by the product. TMi has also created a song around the campaign called Nurdle Shmurdle.
Every ad will drive viewers to the Aquafresh and Cartoonito websites, where the campaign will continue to be supported.
Both the ad and the lyrics of the song are to be posted on the sites in order to encourage further engagement with the target audience.
Adam Eagle, director of sponsorship and promotions at TMi, said: "We commissioned bespoke research via our consumer insights team to ensure optimum targeting and efficient execution. The result is a dynamic campaign."