NGSS 3rd - 5th grade states:
Organization for matter and energy flow in organisms
Animals obtain food they need from plants or other animals. Plants need water and light.
Food provides animals with the materials and energy they need for body repair, growth, warmth, and motion. Plants acquire material for growth chiefly from air, water, and process matter and obtain energy from sunlight, which is used to maintain conditions necessary for survival.
For 4th grade I usually teach this by focusing on owls, where they live, what they eat, how they digest food, their characteristics, etc. I order owl pellets. We use goggles and gloves, and a dichotomous key (which can come as part of the owl pellet order.) The dissecting part will take two class periods if we have only 30 - 45 minutes. Then we try assembling the skeletons as best we can and glue them to a sheet of construction paper. We label the animal, bird, vole, shrew, mouse, etc. Then we graph how many of each animal that contained in the owl pellet. We discuss what those animals eat. Eventually, we work down to producers. We then combine that data from each group. We discuss what would happen to the owl population if one of those animals was extinct, now how about two of those animals? Who eats owls? What happens to them if the owls have no food supply and become extinct?