I agree that building circuits is absolutely necessary to get an intuitive feel for electronics. And certainly for an 8 year old what you did is the best start in electronics. I think I was 10 or so when I got my first electronics kit. But I stayed away from radios, and I have to confess that even now I consider anything that has to do with RF as some kind of black magic. I was just happy to make things beep and blink.Excellent question, with a very simple answer.
The way to get GOOD at electronics is to just BUILD a lot of circuits. There is no shortcut to this. I was building crystal radios and motors when I was 8 years old. I don't know any other way I would have gotten the intuitive feel for electronics.
Good luck, my friend!
Eric