You have a lot of options for excellent little starter kits for electronics of all kinds. But if you're looking to teach a kid about programming, the Kano Kit is a fantastic new option.
The Kano kit comes with everything you need to build a computer (except a monitor): a Raspberry Pi Model B, Wi-Fi adaptor, wireless keyboard/mouse, case, SD card, speaker, power cable, HDMI cable and software. Unlike other Raspberry Pi kits, the real sell here is the software itself. The Kano OS is an incredibly fun little operating system that teaches you all about basic coding with tutorials for making music, games and more. When you finish tasks, you'll win badges for accomplishments. Within a few minutes, you'll have access to the command line and be well on your way to building this little computer all by yourself. I'm an adult and I had a blast running through all the tutorials, so I imagine kids will feel the same way.
Likewise, the Kano operating system is really solid for kids. They will have access to the internet, YouTube, and Minecraft on top of the tutorials. They can also upload their own work to share with other Kano users. The hardware itself feels good. The case is solid, the keyboard/mouse feels like it could take a beating, and the accompanying instruction books are all well made. If you already have a Raspberry Pi set up, you can check out the operating system on their site, otherwise the full kit retails for $US150.