For my son's second birthday, we had kids of all ages. One thing we did was make your own pizzas. I had English muffins, pizza sauce in a squeeze bottle, and lots of pizza toppings. The kids made their own and we baked them right there. (Although I had fancier food for the adults, many of the adults made pizza too.)
Since I do origami, I had made up a bunch of paper airplanes of different styles. The kids went out back and had contests to fly them around. A simple airplane book was all that took.
After that, we did start doing just family activities though. Now we do a family trip in place of gifts around his birthday. Since he's older, he now picks what to do. We've done football games (pro and college) and two-day trips to zoos and museums he's picked. This fall he's going to his first rock concert (bands are parent approved, of course) and he's really excited about that.
Those are some ideas I've used. Good luck.