Hi Michael and welcome to QRPC!
QRP radio would be a great way for you and your son to go to get into radio as it adds a dimension that QRO doesn’t; it lets you get out into the countryside with easily portable kit and easily home-brewed antennas and enjoy playing radio.
The question of ready built v kit construction is a hard one to answer. The ready built option gets you on air with no hassle. Kits come in a wide range of options – some involve soldering every component, winding torroids and aligning, while others simply involve modules that have to be connected with little or no soldering and minimal alignment.
What you go for depends on how much money you want to spend and how sophisticated you need your radio to be.
72, Dave