How do you keep & care for 'pet' caterpillars until they turn into butterflies?

My son %26amp; I 'captured' 3 caterpillars that were devouring my pansies. We kept them in a jar w/ sticks to climb on, %26amp; fresh petunia buds %26amp; blossoms every day, in hopes to keep them until they turned into butterflies. I figured that it would be easy because we already knew what they ate, right. At first, it was fine, they ate good, etc. But 2 of them have died %26amp; the other one doesn't eat anymore. He just constantly climbs %26amp; burrows around like he's looking for something. What are we doing wrong?

How do you keep %26amp; care for 'pet' caterpillars until they turn into butterflies?
Sounds like your remaining caterpillar may be looking for a stout twig-and-leaf combo [leaf for shelter, twig for attaching to] to start spinning himself into a cocoon. In the wild, they'll stick themselves motionless for a bit on a twig or wherever and then spin out some gossamer-like strands and voila, a little white-gray lump on a twig is what they become. Left alone until their inner clock says "Now!" eventually a butterfly emerges to great acclaim, huzzahs, etc. Were I you, I'd take your caterpillar back out to from whence he came and let him get on with it...in his own environment, he might need a different sort of twig than his keeper might select for him.