Q: How can I lock specific apps on my iPad?

The only thing I know of is to use Guided Access to lock a specific app before you give the iPad to a kid. It only works for one app at a time so you'd have to unlock and relock if a new app was needing to be used.

Hope this helps!

~Joe

Your only global options are those in the Restrictions settings.  Individual 3rd party apps can be locked, but ONLY if the developer of that app included that feature in their app.