Whenever I see an app from Preschool University for free, I download it right away. They generally put out pretty good quality language arts apps. ABC Spelling 1 app (linked above) is about learning to spell 3 letter short vowel words. I like that you can adjust difficulty levels by turning phonetic sound hints on or off and toggling from 3 letter display or offering the entire alphabet to select from. The words are grouped by vowel sounds which is great if you are working on a specific vowel. There is also a shuffle feature which mixes up the spelling practice.
I highly recommend any of their spelling, phonics or reading apps. Click through to their developer page to see their library of apps. There is a wide variety available for free. For Spanish learners, I did notice a few free apps now, but I can’t comment on how good those apps are.
Have fun helping your young learners become great readers!