By the time a child is in year three, he has probably had lots of experience in classifying objects, and even words, by their colors, shapes, sizes, spellings, and other properties. He may even know a bit about how to classify living things into groups: plants and animals; insects and spiders; reptiles, mammals, birds, fish, etc. Second graders are also blossoming in their writing skills, learning how to write both fictional and informational texts.
A great way to combine your child's natural curiosity with his developing classification and writing skills is to have him create field guides. Whether it's a field guide for the park, the woods, or your own backyard, your child will gain a new appreciation for the living things around him, while at the same time getting lots of good practise developing those year three language arts skills!