Robbin,
To explain it as simple and basic as possible….
Place the video with the animation with the blue screen on the first timeline and the video with your son on the second timeline below it…..
Then in videofx choose the ‘chroma key’ filter and drag the preset
named ‘pure blue screen’ on the video with the animation with the blue screen.
You should immediately see something happening…from there now, just
toggle the sliders until things look how you want it to. (just hoping iam reading your description correctly).
However for a more professional and believable look it involves more
adjustments and the use of more filters including “chroma blur”.
So what i have instructed above is the basic to get you started and
you start experimenting from there.
Steve Rhoden
Creative Director
TNX EFFECTS STUDIOS.
http://www.youtube.com/hentys