Teaching giants (Kenmotsu) on parallel bars, for me, is the same as on horizontal bar: maximize the downswing, optimize the upswing (by shortening the body).
For athletes small enough to be able to not bend knees through the bottom, they can be very similar.
I’ve seen kids do a series of 5 giants very much like horizontal bar. Their coach (Kelly Manjak) experimented with giants to “Tkachev” (reverse straddle cut to handstand) with one of the boys.
There are two main differences between horizontal bar and parallel bars:
athlete normally will release and regrasp at the top of the swing
most gymnasts find it more difficult to hold on through the bottom of the swing
The first is the lesser problem. Start by spotting giants without releasing. (Gymnast ends up in an unusual grip.) Add the release and regrasp much later.
The psychological barrier of fear of slipping is more likely what will stop boys from swinging aggressively.
Two tips on parallel bars:
Canadian National Coach Edouard Iarov taught me not to spot the hand on the bar — which was common practice where I coach. This is the giant, he told me. Once a boy feels confident he can “hang on” to the bars, learning the giant is easy.
Secondly, introduce giants facing out on the end of the parallel bars. (The opposite direction of the photo.) If the gymnast ever slips, landing on mats off the end of the bar (flyaway) is much safer. It also requires the gymnast hang on as long as possible — to avoid travelling forwards.
Mike Boyd training giant at Taiso. Coach Rhett Stinson.
A study by Spiros Prassas (somewhat outdated) includes photo series and video clips: Giant Swings on the Parallel Bars
Gymnastics Coaching.com 