Is the Fire HD 8 Kids Edition worth it over a regular Fire HD 8?

For a child, yes. You get the protective case and a two-year guarantee that covers accidental damage, which a standard Fire HD 8 does not include. The tablet itself is the same, so adults gain nothing from the Kids version.

Can it run Google Play apps like YouTube and Gmail?

Not out of the box. It uses Amazon's Appstore, which lacks Google Play and several Google apps. Some apps can be sideloaded, but the process is unofficial and not all of them work well.

How much storage does it have and can it be expanded?

It ships with 32 GB of internal storage, and a microSD card adds up to 400 GB for downloaded videos, games and photos.

What does the worry-free guarantee cover?

It covers accidental damage for two years. Amazon replaces a broken tablet rather than repairing it, and the process is handled through Amazon support.

Is the screen good enough for reading and video?

It is fine for picture books, streaming and simple games. The 1280 x 800 resolution at 189 ppi is noticeably softer than 1080p tablets, so small text and detailed games look less crisp.