Nothing beats taking a kid fishing(especially for the first time!). The keys to a great first trip and a lousy one are pretty simple. Follow these couple tips and most of the time a kids first fishing trip is one they won't forget!
1. Don't take it to serious, and don't worry if their patience level is only a few minutes.
2. Try to pick an easy to catch species to target. KIds, most of them anyways, don't care what they catch. They just want to catch SOMETHING.
3. Make it fun and keep smiling. If the fish aren't biting and swimming or playing in the park sounds like more fun, do that; the fish will be waiting for you next time!