Bukkit plugins require running a separate server and giving the kids access to the server. Doesn't seem as practical as a client mod if you're trying to make it kid friendly.
The author mentioned It makes it possible for Minecraft Server administrators to create interesting places for players to come and play.
I agree a client mod is a great place to have this functionality, but if it is being done on the server as well then using a framework like Bukkit is a great choice.
For one thing, the author complained about obfuscation making it difficult to expose different functions in the game. Bukkit provides a stable API, so it makes sense for a scripting wrapper to expose those functions, and by doing so gain a lot of functionality.
I've implemented ScriptCraft as a bukkit plugin now. Bukkit's API and plug-in deployment mechanism is sweet. ScriptCraft and Bukkit are really well suited.
