For kids you might want to do something to keep the top attached to the box - otherwise they'll lose it. On the slide top you could glue a piece into the top of the box (the inside of the sliding part) that hits the box side when slid open.
Here's a box that is a kind of ring cut made from a 2x4. You can probably see how it is cut from the photo. It takes no joining - just cut the 2x4, glue on a thin top & bottom (these are 1/8" BB Ply) and shape the fixed part so there's no interference. Then pin it with dowels or small nuts & bolts.
![](https://lh3.googleusercontent.com/-4S-mQuo-HUI/UgOoxzYNu2I/AAAAAAAABUQ/PwRcKVnOv7k/w811-h903-no/2x4%2Bflip%2Btop%2Bopen.jpg)
![](https://lh4.googleusercontent.com/-RMt03BuGkr4/UgOoy36W47I/AAAAAAAAA1A/qz5aSeYOiHA/w1490-h729-no/2x4%2Bflip%2Btop.jpg)
Here's a regular ring-type box, but the top comes off so it might get lost. The rings are 1/4" thick. It's cut from a 1x4 - any length you need. A 2x4 could be used if you want it deeper.
![](https://lh6.googleusercontent.com/NjljUnrkAtYEa_WKT69e3SdJJlz3GhbCtC9uZgi2hBQ=w365-h336-no)