My dad taught us loads when we were kids, every Sunday morning up at the crack of dawn and we would be off for hours, he would never let us pick up anything or take anything too, but he would show us birds nests with eggs in and chicks, then on the way back we would get the mushrooms for breakfast.
One of the best nests I can remember was a robin's nest, it was built right near the ground in a old tree trunk but there were these small blue eggs.

Many happy memories.