I agree with Alaska Man's solution and would comment there but I want to add considerable detail that won't fit in a comment.
To do what he's suggested, get a subject to stand in the bright sunlight. Choose 2 of the following values - ISO, shutter speed, aperture - based on your needs. In this case I would suggest choosing shutter speed and aperture - you want fast enough that your subject is not blurred due to motion (so, perhaps 1/250 at a maximum, but 1/500 or 1/1000 if you can afford it without losing too much light - see notes later) and aperture perhaps around 8, to keep most of your subject in focus. Now walk close to your subject and fill your frame with a sunlit portion - eg. their shirt. Allow camera to choose appropriate ISO using in-built meter. Note this.
Now switch to manual and key in all same settings. Your shutter speed and aperture should be set. Key in the ISO the camera picked. Now over-expose one stop. The meter produces an average grey but there is room to overexpose one stop - so if you managed 1/1000 (without the camera maxing out on ISO at that setting), then drop back to 1/500, for example. This technique is called exposing to the right or ETTR - you can search for more info.
Ensure your camera is shooting RAW. Now go take your shots focusing on whatever you like.
What happens is that the camera will expose correctly for your highlights in each shot. It should not blow out (even with overexposing 1 stop). In your post-processing you can bring the exposure back down to mid-tone greys if needed. The purpose of ETTR is that your sensor is more sensitive at the bright end than what it usually shows in the jpeg preview you see on the camera's LCD screen after you have taken the shot, so we want to capture light as brightly as possible without blowing out. You can never really recover an image that's blown out. And if you underexpose and start with a dark image, it looks bad - usually noisy, or large blocks/regions all the same tone - when you bring the exposure back up.
The shaded portions of your shot will appear very underexposed though. That's the nature of the extreme conditions you are shooting in. However again, in post processing, you can bring up the exposure in these regions. It won't be a superb result, but you're working within difficult constraints - dappled, high contrast, rapidly changing light with moving subjects (and likely moving photographer also).
I think the above is your best shot at getting usable results. Many times in these scenarios where lighting conditions are poor, a relatively poor colour photo can be salvaged as a usable black and white image. Bear this in mind.
Finally, if it is also cloudy, bear in mind that if the cloud cover comes over, then your highlights have been darkened by cloud - you will need to re-expose (or make a best guess by opening up a few stops). Notice if the cloud clears again - now the highlights are brighter again and you will have to re-expose for the highlights (or switch your best guess back down a few stops).
The reason for exposing for the highlights is that this is how our eyes naturally work. When we look at a sunlight scene - no part is blown out. When we shift our eyes to a shaded scene, they adjust, and the brightest portion is resolvable. Getting the brightest part of your photo exposed perfectly is how our brains expect our eyes to render a scene - so it looks natural for the highlights to be well exposed, and everything else to be defined by darker shades.
All the best! :)
PS. You might find your camera pushed to the limit in these conditions. You might find the meter has to choose the highest available ISO and you still get dark shots. In this case, open up your aperture wider, with the understanding your focus is going to be shallower and for many shots you may not have focus on eyes. Or make your shutter speed longer, understanding you may get motion blur. A great exposure may just not be possible :(