In Lord of the Flies, Chapter 3, what quotes demonstrate how the boys have lost their innocence?

Some examples of the loss of innocence at this point are Jack’s insistence on killing a pig and Ralph's inability to get anything accomplished. 

Jack wants to kill the pig, and it is more important than anything.  He is not interested in building shelters, and fights with Ralph about what is more important.  He also does not seem to care about being rescued.  He just wants to kill something.  It is not just about...

Some examples of the loss of innocence at this point are Jack’s insistence on killing a pig and Ralph's inability to get anything accomplished. 

Jack wants to kill the pig, and it is more important than anything.  He is not interested in building shelters, and fights with Ralph about what is more important.  He also does not seem to care about being rescued.  He just wants to kill something.  It is not just about the meat. 

“Rescue? Yes, of course! All the same, I’d like to catch a pig first—” He snatched up his spear and dashed it into the ground. The opaque, mad look came into his eyes again. Ralph looked at him critically through his tangle of fair hair. (Ch. 3) 

The childishness of the fun of being alone on the island with no adults has also worn off.  The boys are unable to create a stable organization and get anything done.  They have not hunted and gotten meat.  They can’t get the shelters built.  

“All the rest rushed off. He’s done as much as I have. Only—”

“Simon’s always about.”

Ralph stared back to the shelters with Jack by his side.

“Do a bit for you,” muttered Jack, “before I have a bathe.”

“Don’t bother.” (Ch. 3) 

Arguing is common.  Jack and Ralph, the two leaders, are at odds.  Jack wants to lead the hunt, and in fact has been assigned to do so.  Ralph chose him for that because he knew it was something he would agree to.  Ralph is failing as a leader though.  There is not enough power in the conch to extend beyond getting people to listen at the meeting.  The little kids are afraid there is a Beastie on the island.  Simon does in fact go off on his own, having his semi-religious experiences in the jungle deep inside of the island.