Leave the Frisbee and pick-up football games to the kids. A family-friendly barbeque offers a calm spot to rest under an awning or large umbrella to keep the elder out of the sun. Bring a comfortable chair for fragile elders and a footstool to raise their legs if appropriate. Elderly family members sometimes feel forgotten at events like this, so be sure to set up a rotation of people to sit a while and chat.
For the more active seniors, fun backyard games like croquet or badminton are just the ticket. They can even get involved in water balloon tosses and Frisbee games. While the older generation may not be diving on the grass to make a catch, they can still have plenty of fun.