Children will visit Britain's major museums and galleries free of charge from April under a "new contract" with the arts announced by Culture Secretary Chris Smith.
But some institutions fear the Pounds 100 million plan could jeopardise educational programmes currently funded by admissions income.
The funding increase will see charges scrapped at national institutions which currently charge up to Pounds 3.50 for children. The open-door policies of those who do not charge for admission will also be protected. The scheme will allow free entry for all by April 2001.
Mr Smith said: "The whole thrust is to make sure as many people as possible can experience the arts and have access to the great collections we have in this country."
But Dr Neil Chalmers, director of the Natural History Museum, said: "We would lose aroundPounds 6 million if we stopped charging for admissions. If we don't receive that much from these extra funds we would be hard-pressed to generate that much extra business ourselves."