2yr old was jumping on bed, fell &suffered a greenstick femure fracture he showed no signs of distress or pain.he even took a2hr nap after then woke up with discomfort.how is that possible?

Kids are resilient: Kids are pretty hard to brake. I suspect he probably had some pain which prompted the xray. Kids have a thick outer lining around their bone called a periosteum. This makes it very pliable unlike adults where it just cracks. Just like a green twig when you break it in the spring, a greenstick fracture is very similiar. He should do fine and will likely be healed in next 2-4wks.