It's especially bothersome to me when parents use "learning" apps to try and pretend that they're being a more productive parent by giving their child an iPad. Perhaps they can do some good, but their effects are also vastly overstated and are no substitute for hands-on physical teaching by parents.

Here is an example study that tries to test the effects of apps vs. parents teaching foreign language words: https://www.ncbi.nlm.nih.gov/pubmed/20855901