Nature study happens outdoors. Read a short chapter together, then go and look for the real thing, in your own garden, a park or a hedge, in whatever season it is now. Spring is for nests and flowers, autumn for seeds and spiders. Give each child a nature notebook for drawing what they find, with the date and the place, and a few words about it. Over a year the notebook becomes their own field guide, and that one habit does most of the work.
Look, but do not take or taste. Never eat a wild plant, berry or mushroom, leave nests and eggs alone, watch stinging insects and wild animals from a distance, and wash hands after handling soil, ponds and leaf litter. These books were written a hundred years ago or more. Plant names have changed since, some animals are rarer or more common than they were, and the stories in the read-alouds make the animals talk, so talk together about what is story and what is fact.