The group says that none of the top 20 shows viewed by 4 to 15 year-olds would be covered by Ofcom's proposed Viewing Index, which takes account of the proportion of children watching rather than actual numbers.
In a two-week period in October, the most popular show with the age group was Ant & Dec's Saturday Night Takeaway, with over one million viewers aged under 16, followed by Coronation Street, Emmerdale and The X Factor.
The highest-rated show aimed exclusively at children was SpongeBob Squarepants, the 27th most popular show with 170,000 viewers.
Which? said Ofcom's plan was "a missed opportunity" and urged the regulator to reconsider a 9pm watershed as a viable alternative to the proposed route.
Ofcom has given interested parties until 28 December to respond to its proposals and plans to implement the self-regulatory restrictions from the end of March 2007, with dedicated children's channels allowed a transitional period until 31 December 2008.
Among the companies taking steps ahead of the ban is Burger King, which will withdraw UK advertising during children's programmes from tomorrow (22 December).
This article was first published on Media Week