Universal won the business following a five-way pitch against rivals that included OMD UK and Mediaedge:cia. The business was previously held by Equinox.
Sarah Mieran, Nickelodeon UK's senior marketing manager, said: "We operate in a very competitive sector and felt Universal McCann offered an understanding of our market and some genuinely innovative ways of talking with our audience and building our brand and viewing levels. We liked its integrated, imaginative, results-focused approach to our business."
The children's TV sector, worth up to £100 million in advertising revenue, will become increasingly competitive when ITV launches its dedicated children's strand on ITV4. The BBC, with its CBBC and CBeebies channels, is the largest player, although Nickelodeon is the biggest commercial children's network in the UK. Its channels comprise Nickelodeon, Nick Junior, Nicktoons and Nick Replay.
The media appointment does not affect Nickelodeon's creative roster, which includes Mustoes and Walsh Trott Chick Smith.