The problem was that in that era most child actors tended to lose their popularity with audiences when they grew up In her case, it's unfortunate because she was a very good actress .John Agar's only claim to fame was that he was Shirley Temple's first husband.
He was not actually bad in small supporting roles , as long as they were small! He was in 3 John Ford movies ,Fort Apache, She Wore a Yellow Ribbon and Sands of Iwo Jima.
He took acting lessons but they never took!
He found his groove Revenge of the Creature (1955)…. after that is became the king of the Z film.
Funny thing was that Shirley Temple , who divorced him in 1950, never could shake the childhood movies. She was a good enough actress but quit film in 1950 , did do TV work for some years but was never given much in the way of roles.