Pick a warm, sunny day when they'll be out to sun themselves. In the spring, the younger ones will stay together around the holes, my uncle has had a lot of sucess with a .410 from the pickup window like this. If you can whistle like they do, or reproduce the sound somehow, you'll have better luck getting them out. They can't resist standing straight up and answering! I can't remember for sure, but I think they're cannibals as well (stops tunnel pluggage for those that die underground). If you move from a spot where you killed a few, come back later to check for more.
If you want something different and fun for the kids try this; Take a fishing rod and tie a slipknot in the end of the line. Place the slipknot around the hole, using small rocks to keep the loop on the ground around the opening. Back-off with plenty of line (40ft+ in open country) and whistle (high pitched, even tone, half second on, 4 sec+ off. You know, like they do!!) When he pops-up, jerk the rod back and you'll suck him right out of the hole!!! Keep reeling real fast and he shouldn't get away. Have a pair of welding gloves for grabbing them, they can bite damn hard and carry disease.
I did this for a neighbor in town that had a gopher problem. He was one of those guys who had the imaculate lawn. He tried poisons with no luck. I was 12-13 at the time and he laughed while I was setting up. You should have seen his jaw hit the ground when I arced that gopher from his backyard to mine!!