Earning a nomination at an early age is more prevalent in the supporting categories because their players tend to be cast in younger screen roles. The Academy voters are also less discriminating in appraising performances by children and teenagers–sentimentality has always played a considerable role.
Children have been nominated for Oscars ever since the Supporting Acting Oscars were created in 1936.
Bonita Granville
Granville was the first child to earn a nomination in 1936, for These Three, based on Lillian Hellman’s 1934 play, The Children’s Hour.
In 1962, two young girls competed for the Supporting award: Patty Duke (The Miracle Worker) and Mary Badham (To Kill a Mockingbird); Duke won, thus becoming the youngest Oscar winner to date. Her record was later broken by Tatum O’Neal.
The same situation prevailed in 1973, when Tatum O’Neal (Paper Moon) and Linda Blair (The Exorcist) were Supporting Actress nominees; O’Neal won.