Robert Downey Jr. used to sing in shopping malls.

The 'Iron Man 3' star - who has son Exton, two, and three-week-old daughter Avri with wife Susan Downey - decided to help raise money for music education by producing a series of impromptu concerts, Playing It Forward, which is a collaboration between his company Team Downey and online entertainment distributor Crackle, because he believes joining an a cappella group as a teenager helped him to develop the confidence to carve out a career in Hollywood.

He explained: ''When I was growing up, it was a given that if you wanted to have that initial exploration into music, it was readily available to you - regardless of what was going on with the economy or state budget. Clearly there has been a shift in that.

''We are hoping to make you want to stop on the street and listen to the message. As a kid, I played the drums and piano, and late, when I went to Santa Monica High School, I joined an a cappella group and sang at malls during the holidays. That's what ultimately gave me confidence as a performer. All kids should have the opportunity to be exposed to music.''

Playing it Forward - which launched in November 2013 - features surprise street performances across the USA from some of the biggest's names in music, including John Legend and Imagine Dragons, all benefiting music education and charities of the artists' choice.