The title indicates the number of young people in England. It will be unveiled today by children's minister Beverley Hughes. The rebrand is expected to cost £93,000.
Sir Al Aynsley-Green, Children's Commissioner for England, said: "11 Million emphasises our purpose, our priorities and the central role of children in guiding our work."
But Simon Burne, senior consultant at Think Consulting Solutions and former chair of the Institute of Fundraising, said he "wouldn't have a clue" what an organisation called 11 Million did.
"The danger is they undermine their gravitas in the places where they are known, without necessarily improving their ability to reach out to the people they are representing," he said.
Mike Barnato, managing partner of consultancy Strategy and Marketing Partners, said the name could be "aimed at appealing to the YouTube generation".