Get them an age/reading-level-appropriate magazine on some scientific topic.
Ranger Rick (National Wildlife Federation) is good for kids interested in nature.
Monthly magazines with puzzles and games are good for the math/logic-type geeks-in-training.
Comic book subscriptions and fannish magazine subscriptions are good for people whose geekdom is in literature, TV, or movies.
Why paper in the age of digital media? Because it's concrete and tangible, and it still works when the Internet or electricity goes out.