Look For Ways to Stabilize Them
Let young tots into the great outdoors, and you may be running around in circles trying to bring them back together again. So when photographing outside, try to pick a spot that has something they'll both gravitate to — stairs, a slide, a bench, a jungle gym, etc. — and encourage them both to hang out there. They might not be willing to spend an hour there, but they'll likely stay there together just long enough to get a few key shots — just be sure your camera's ready!