Aristotle divided all living things between plants, which generally do not move or have sensory organs, and animals.
In Linnaeus' system, these became the Kingdoms Vegetabilia (later Plantae) and Animalia. Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these are still often considered plants in many contexts. Indeed, any attempt to match "plant" with a single taxon is doomed to fail, because plant is a vaguely defined concept unrelated to the presumed phylogenic concepts on which modern taxonomy is based.
.. so back to the "simple" answer.. for the eight year old.. (without being "doomed to failure"...)
animals have independent locomotion and sensory organs
plants generally have no independent locomotion nor sensory organs... (and there are some exceptions...)
.. but for me the food one works pretty well! (Can a venus fly trap live without photosynthesis?)
science ... like the rules of spelling, has exceptions!