This article assumes you know how to create a restriction profile.

To enable dictation on a device you should have the following 2 options checked in a restriction profile;

• Allow Dictation
• Allow Siri
  • Allow Siri while locked

Dictation will not work if either restriction is unchecked.

Enabling dictation on the device:

By going to Settings > General > Keyboard and Enabling Dictation you should get a microphone button on your devices' keyboard:

When you press this button you'll be able to dictate on the iPad.