Have a look at
AC 61-98A on how to conduct BFRs, if you aren't already familar with it.
Looking for the above I came across this nice
FAA slide show on the subject.
AOPA deals with getting back into flying
here. (You may need a membership to see it.)
After you decide what topics to cover based on what he plans to do with an airplane, you must get him up to speed on all or most of the basic manuevers so he has adequate control of the aircraft and a feeling for how it flies. The private pilot PTS is the reference of course and I would hold him to being able to do most or all of the manuevers to standard. You may save his life so don't take take an "I'm your dad" kind of attitude about from him on this. He should be able to nail the manuevers in the PTS, or he can go to someone else who will definitely insist on the same thing. Theoretically the number of hours for reaching the standard could be quite high. I would be suspicious of someone who says "I'll get them together on my own, just give me the signoff." Now is a good time to get them together. There is no provision for expired recency requirements that allows practice solo flight, so you should be along for all his practice until he is ready for the signoff. Hopefully that will only take a small number of flights, it may or may not.