Smileyguy...........'I appreciate all the help up to this point, some very good advice. I would just like to reign in this thread a wee bit before we get too far off topic and on to lighting. I shoot with natural light, no flash--fill or otherwise--so lighting is not my concern in this particular instance.'......
..............How's it going?. Hopefully you'll take my comments as intended, which was to unload a few thoughts to Johnny Walker who as opposed to you is considering 'fill flash',..........I've certainly no wish to get off topic, but he's here, and expressed his considering going down a certain road, and I though it woundn't do any harm in giving him a few of my thoughts on the matter.
.....AND RETURNING to the initial topic
, I started out my serious photography photographing in McArthur park in LA, that was with a Nikon FTN, with a Vivitar Ser.1 35mm-85mm varifocal lens, just me and the camera, no reflector, flash, no nothing.
Doing it this way for quite a long time, taught me something about biasing exposure one way or another to encompass a mood, or compromise between foreground/background/different parts of a scene/subject matter that's being hit by varying amounts of illumination.
If I can add to some of the suggestions you've already gotten, when I'm photographing a family for my portrait business, and they want the illusion of the spontaneous, I'll sometimes suggest going down to park to where the childrens playground is, and having the whole family go down the slides, or all together pushing a family member on a swing, or helping helping each other 'leap frog', or helping each other pull themselves by their arms along overhead bars.
You can come up with venues and events like these and get the family so wrapped up in having fun together, your biggest problem will not be getting them to have fun/smile/pose, but keeping up.
Lastly, with these kinds of shoots, it will be impossible to plan everything, nor should you want to, since you'll be coming up with ideas as you go along.