The app ( on the iphone ) Duolingo works very well, you can do 5 - 10 mins a day ( more if you want of course )
My oldest daughter has learnt Spanish ( though she is doing this as a GCSE in school, though the teacher said she could sit her GCSE now in yr 9 as she has picked it up so well, i didnt have the heart to tell him it was the app ) and French in the last 3 years with it, now moving onto Polish
its a free app , Duolingo