The biggest UK children’s labels are from within the BBC label, and from EMI’s HMV sub labels, such as HMV Junior Record Club. Capitol also used the ‘Junior Record’ tag. Many labels released children’s records as part of their normal output. C They will be elsewhere.
There are a number of smaller children’s and spoken voice specialist labels, as well as labels devoted to sound effects.
Some are collectible by association … Century 21 Records and Gerry Anderson cartoons, or the Disney labels.
Others, like sound effects of trains and racing cars remain sought after, perhaps more at Toy Fairs than Record fairs. Yes, people do play them while operating model train layouts or Scalextric.
Then many spoken voice ones have the original authors or poets, or famous actors reading them.