Using the most up-to-date f-droid version, go to “Games Category”. Skim through available apps, as there are a few select games that are suitable for pre-K; with more becoming with increase of child’s age.
It may be necessary with f-droid to install an app to know what its function really is , since descriptions and screen shots aren’t always clear or direct.
Here are some personal favorites which I use with the family
GCompris 
(GCompris education suite/many learning games for 2-10yrs) - GCompris | F-Droid - Free and Open Source Android App Repository
Nounours and friends 
(Manipulate a teddy bear with a swipe to do funny things) -
Apple Flinger 
(Funny single- and multiplayer game - Use a slingshot to shoot with apples)
Seafood Berserker!
(Help the Vikings repel a fish attack!)