I don't have much experience with beginning level language apps since I didn't learn Spanish this way but I did survey a couple that might be helpful. Personally I use Brainscape to memorize large amounts of words in relatively little time but if your son isn't that motivated, he could try Spanish Touch Trainer
https://itunes.apple.com/us/app/spanish-touch-trainer/id395126280?mt=8 . It's 3 dollars and it will help you with basic translations in a fun way. I believe this will help in both vocabulary acquisition and pronunciation since a really nice female voice reads back the sentences to you after you translate them. My opinion is that it is good for beginning and low-intermediate students. Brainscape has a premade Spanish vocabulary pack that costs 7.99 in-app purchase but this is suited more toward AP Spanish students. There are about 20 decks. In the beginning you will find very basic words that are appropriate for beginners but toward the end it gets much, much harder. I'm sure I have a bunch of apps in my purchases history that I could suggest but my list of purchases doesn't seem to be showing up at the moment. Another popular app for learning Spanish is Spanish Anywhere, though personally I never found this one to be that useful and it is more expensive than the rest - I bought it for ten dollars a few years ago, not sure how muchit is now.
Another one is Salsa
https://itunes.apple.com/us/app/salsa-spanish-language-learning/id444645338?mt=8 , seems to be similar to Spanish Touch Trainer except it has no pronunciation. Try the lite version before upgrading to pro.
