I’ve found that short hikes that have destination (waterfall, mountain view(s)) have been a success, as well as anything that allows our child to engage the environment along the way (rock or tree climbing, plant identification, animal identification).  Also, allowing them to explore the world on their terms helps.  On our last trip to Mt. Rainier, we paused frequently on hikes to let our child play in the snow, build rock cairns, and take pictures and that seemed to make a bigger impact on his experience.