You mean you try to get the movie file from your son's pc to your mac. Or are you trying to get THE movie from THE Flip right away to your mac, cause if thats THE case, I would first place it on your son's pc and then transfer THE file to your mac. E-mail wont do, you can only send 10 mb files by mail.
Best way would be a website where you can drop THE file. Something like drop.io or whatever, Google for Some websites.
You could also create à YouTube account, then let your Son upload THE movie to YouTube. Than you can download THE original file again from THE YouTube account. But you'll have to share THE account and password.
When THE file is too big try to see if you can convert it into some h.264 (or h.265) codec, avi or mp4 or mov should be okay as THE container.
Good luck, sorry for THE annoying writing Style (all THE capitals and such) but THE iPod touch thinks it can spell better than me, it's freaking annoying.