a son who doesn't mind getting dizzy on the carroussel.
Set your camera on S or TV and select a shutterspeed of half a second and
work from there. Maybe you will want to go faster if you don't have a
stabelized system or slower if it looks better or if you are working with a tripod.
turn on your little flashy thing on top o' the camera and set
the second curtain flash option. This is important for a natural effect.
Try out the difference between first and second curtain for yourself.
experiment with the shutterspeed and you'll have hours of fun or until your
kid is sick of the swing or you wich ever comes first.