Kids mobile app UX

My company's main product is a mobile application (Android & iOS) that provides kids content (interactive stories, videos, coloring, games) for kids between 3 and 8 years old.

We're still struggling with providing a UX that is easy for kids and understandable as well. We also have a few new features we'd like to add.

Taking into consideration that we don't have a UX expert:

  1. What is the best approach/ place to find one?
  2. What should his skills be (graphic design? kids apps experience?)
  3. Should we hire a full time UX expert or just find a consultant who will do it as a one time gig?