Yes, Toontastic appears to be the best app to use and it was developed by Google.

There's the typical video production apps like FilmoraGo or KineMaster, but these aren't strictly animation; you couldn't make an explainer video with it if that's your goal.

If you're instead looking to design an app for Android, you'll want to look at Figma and Adobe XD. Figma has some pretty good prototyping too.

We use Figma for most of our UI animations at Vidico. See most of the examples of the homepage for an idea of what I'm referring to: https://vidico.com/

Giving names of few useful applications relating to animation software programs is not the ultimate solution. You must understand something else as well. It is always a good idea to compare multiple apps that serve a given instructional purpose. I will advise against simply selecting the first app or the most popular app as you, or your students, have specific needs and your app needs will be unique to your circumstances.
Here are few useful animation software programmes:
1. FlipaClip
2. Adobe Spark
3. Animation Desk Classic
4. PicsArt Animator
5. Animoto Video Maker
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath