The very first really big kid actor, even before Shirley Temple, was Jackie Coogan (October 26, 1914 - March 1 1984) He started out at as an infant in Vaudeville and in film. Charlie Chaplin was impressed with him and cast him in The Kid (1921). Needless to say, he became a huge star. But as is the case with child actors, as he got older he became less popular. He earned about $4 million, but unfortunately, his mother and stepfather wouldn't let him near his money. Remember, back then, there weren't any laws to protect child actors and in the end, all he got from them was 126K.
There are two things I should mention about Jackie Coogan. One is that because his mom and stepdad riped him off so badly, the California Child Actor's Bill was enacted, which makes it mandatory that 15% of the child actor earnings be put in in a trust for the child (etc).
The second thing is that Jackie Coogan later played our beloved Uncle Fester on the Addams Family!!!