I did this very thing for my family reunion back in July. I took a 6-foot 2X2, sanded smooth, and painted one end (to keep track of whether it had flipped when thrown). It's light, long enough, and durable enough for kids to abuse.
For the hammer throw, I bought 6" styrofoam balls and stuck 18-inch long 3/4dowels into them to resemble an oversized lollipop. The kids threw these for distance, and there were no worries about hammer claws or mashing toes. If you use this idea, make sure you glue the dowels into the balls. Otherwise they'll come apart when the kids throw them. I learned that the hard way.
If the weather is warm enough, the kids will enjoy a Wellie Toss. Take a rubber boot and fill it halfway with water (or more if they can handle it), then have the kids throw it for distance. At my reunion, the adults threw them. The men's winner was 50 feet even, and the women's was 49 feet and a few inches.
Something I didn't think of in time was how to score the caber toss. Alan H. or some of the other athletes here can tell you how the points work. I went with whoever was closest to 12:00, then next closest and so on. We gave 1st, 2nd and 3rd place prizes, and each kid got a participation medal.

I hope this helps.