buckworks - 9:02 pm on Jan 21, 2009 (gmt 0)

From the thread title:

video of my son playing a piano song of a popular movie song

Something needs clarification here.

If he is playing a "popular movie song", it IS copyright infringement to publish his performance without obtaining permission from the copyright holder. It does not matter if it's his own arrangement of the music; copyright applies to derivative works.

On the other hand, if it's a completely original composition that merely happened to have the same name, you'd have a case for contesting the infringement claim.

Get advice from a lawyer who is experienced in these matters. The last thing you'd want would be to end up with a "let's make an example of him" lawsuit on your hands.