If a butterfly in a insect what is a Caterpillar?

My duaghter asked me this a butterfly fits the discription of a insect (head thorax adomin and 6 legs) but what is a caterpiller? Orthopod ?|||A caterpillar is simply the juvenile form of a butterfly...its baby. Caterpillars do only have six legs, and the rest are some sort of muscular appendages.|||It's in the same family as butterflies and moths, Lepidoptera. It's not much, but I hope it helps.|||A baby insect...