I think radio advertising in general is not really targeted towards children, television and Internet advertising would be far better use of the advertising budget if you are trying to market a toy to children, it's hard to advertise a toy over the radio because most people want to be able to visually see it.
Radio advertising is not an effective means of advertising children's toys. I believe that it is not effective because, often, the reason a parent will buy a toy for their children is because the children ask for that toy after seeing it. Radio does not provide a visual cue for the child, hence the child will not be inclined to ask their parent for the toy. For this reason, I believe that audiovisual cues such as through television and retail stores would provide a substantial benefit over radio advertising.
Simply put, this isn't 1950 anymore, and Ovaltine isn't going to sell you on a decoder ring over the radio. Children don't listen to very much radio, so you would only be reaching the children's parents. This makes sense, since the parents are the ones buying the toys, but the parents won't know that it is a toy their children want unless the children tell them so. Television (and increasingly the internet) are much more effective ways to advertise children's toys.
There are very few people actually actively listening to the radio right now, especially children, raised by television at this point, who would likely need to see and visually process something in order to garner an opinion on it. And parents probably only listen to the radio during a morning commute, where children's toys will be the last thing on their mind.
I do not believe radio advertising of children's toys is an effective way to advertise these products. I think children respond to visual ads and pictures of toys. Radio ads lack this visual display and thus make it more difficult for the child to understand. Toy companies feel free to waste your ad money on radio, I'd rather not see them, nor do I want my children to see your manipulative advertisements.