I think one of the best investments you could make is to do a bit of research and find out how to make some light modifiers, like large,rectangular (NOT circular!) reflector panels using PVC pipes and fabrics in white, silver lame,and also transparent white fabrics for softening and diffusing natural light or electronic flash. Common words are panel, reflector, scrim, and reflector panel--they all are referring to a frame which has a fabric fitted to it, to either reflect light, subtract light, or to diffuse light. "Scrim lighting" is remarkably versatile,and is an entire discipline unto itself. Simple, and incredibly versatile and variable and suitable for many situations,and actually pretty inexpensive compared to larger softboxes,etc.
To do successful outdoor photography, a person needs to be able to find good light, or to make good light out of marginal or poor light. Reflectors will allow you to fill-in shadows both indoors, and outdoors. Rectangular reflectors are MUCH easier to prop up, or to clamp, and you can make them yourself out of PVC pipe and pipe elbows,and a bit of DIY sweat equity. They are low-cost,but the value they give is very high. Round, collapsible reflectors are very portable, but they do not reflect nearly as much light,and they need special, high-priced grip equipment to get them to stay in position.
A single 42x78 inch reflector panel can be fitted with white reflective, silver reflective, gold reflective, or subtractive black fabric, OR transparent white fabric--all held in place with 4 corner elastics. Look at the Scrim Jim line of factory products. These panels can also be used to bounce flash units off of, or you can shoot flash heads through the panels when the transparent white fabrics are mounted,and you have the ability to custom-adjust the light source to your needs, based on how far the lights are from the scrims. You can even remove the fabrics and place them on the ground,and you can also use the panels fitted with other fabrics for tight head shots. The guy who has the Lighting Magic web site has a ton of free lessons that you might wish to check out.
One of my mentors told me about "scrim lighting" in the late 1970's. It is a commercial photography mainstay,and well worth checking into. It is remarkably adaptable to family photography.
Diffusion Panels