Don't worry! Everything he's doing is completely normal for a piggy adjusting to his new home.
He doesn't know you yet, or his new cage, or the sounds of your house. His entire world has changed, so he has to adjust--- and he will! When he does he'll be calm and friendly once again. How long that takes depends on the piggy.
To help him there a few things you can do. @HunterRose13 gave you great advice! You could also lay a cloth over the roof of his cage. Guinea pigs greatest predators are birds of prey, so they can be very spooky when they don't feel sheltered enough from the sky. Because of their prey instinct, many guinea pigs will always run from getting picked up, but calm down once you cuddle them against your chest. It's best to try and approach them from the front and keep your hands as much at their level as possible. Keep trying to hand feed him--- he'll soon take it out of your hand; don't give up! --- because the key to any piggy's heart is food. Then he'll start associating your voice and hands with good things, like yummy veggies. Green/Red leaf lettuce and Bell peppers are favorite treats; and they also supply the greens and vitamin c that are very important to their diet.
Guinea pigs poop quite often; it's nothing personal, just how their bodies work. It's nothing more than digested hay lol. Just put a towel or something on your lap. HunterRose already said the best way to lessen the peeing/pooping in his house! They'll always do it a little. I just put extra carefresh bedding in there. What kind of hidey house does he have?
@bpatters link is fantastic with everything you need to know. Browsing this forum will give you a wealth of info, and always feel free to ask any questions. This site also helped me greatly as a new guinea pig owner:
www.guineapigmanual.com It's very readable, has funny jokes and cute pictures, and fantastic info. Your kids will enjoy reading it, too! Best of luck