So alien are a thing in Young sheldon.

For context, I haven't watched Big bang theory and directly started watching young sheldon, and btw this show is good and funny and I am loving it.

I just completed S02 EP11 titled 'A Race of superhumans and letter to alf' and in the end scene we see Missy writing a letter to Alf who is a alien and then we are cut to this scene where we see this puppet like alien(or whatever he/it is) So, this means that alien are canon in Young Sheldon.