Batty,
Your son will have a good time and be glad that he chose to go into the IDF. I have friends that went back to the homeland and went in the IDF.
All of them said that they were glad that they went in. All of them definitely grew up, didn't have influences to disrupt them.
He's been there before so he already knows how to get around. Tell him to keep an open mind and his mouth shut! If he comes off as a mouthy American, they'll definitely treat him as such.
Getting through basic is all a mind game, every military treats boots the same. Break them down and then build them back up the way they want them. They don't care how fast they can run, how many push ups.... they want people that can follow orders and think on their feet.
As a treat for going and making it in, get him a good knife. One that's good for the outdoors would be a good idea. That or a good tool like a Leatherman, SOG Power Pliers, SAK....
Tell him good luck and to enjoy himself! See all of the Middle East and other parts of Europe while he's there.