Central to the campaign, which kicks off on Monday 19 July, will be a games promotion.
The Garden Games are based on the basic elements of athletics – running, jumping and throwing – adapted to be played in the garden or local park.
A hundred packs of the Garden Games will be give away for eight weeks via the website, www.mccaingardengames.co.uk.
The Garden Games is a strand of McCain’s estimated £5m five-year partnership with UK Athletics.
Former Olympic gold medallist Sally Gunnell will also provide top athletics tips on the website to help mums get the most out of the games.
A spokesperson for McCain said: "[Murphy is] the perfect ambassador for the Garden Games, which are designed to help mums get their kids active together and, as they are based on run, jump and throw, they are an ideal introduction to athletics."
McCain signed the five-year partnership with UK Athletics in 2008.