When leading a nature walk for kids that young, it's pretty easy to dominate the conversation. I can point out the differences between a daddy long-legs (or harvestmen) and a true spider (daddy long-legs only have one body part; spiders have two). Or I can teach how to identify a maple leaf versus a tulip poplar (maple leaves look like hands, with five points, while tulip poplars have four points and look like tulips).
What I can't teach is how to make a child observe nature. I can't teach wonder.
Wonder is fostered by letting the child lead you. Observation is "taught" through un-teaching, so to speak, by stepping back and letting the children lead the way. When they pick up leaves, you can teach them about leaf identification. When they squat on the trail to study a daddy long-legs, you can talk about the differences between true spiders and other insects.
No lesson is going to be driven home unless the child is engaged. I've learned that you can't teach that, but you can definitely foster it.