If they like art, a guided tour of the Musee d'Orsay or Louvre would make a great gift.

If they like a raucous wine tasting, Chateau O is fun.

Thank you everyone for the great ideas. It was a hard decision, but we ended up booking
http://www.4roues-sous-1parapluie.com/EN/index.html. It sounds really fun and just right for them. (On my next trip, though, I'm going to some of these amazing restaurants.)

Thanks again!

greengiant----I'm curious,which tour did you choose? I checked out the sight and they have some interesting things to choose from.

Michel_Paris what a good recommendation.

An expedition to Giverny in a private car, with plenty of time for Monet's house and garden, a nice lunch and the American impressionist museum would make this parent happy if our children were in a position to afford it.

Have they been to Paris before? Or even if not, a day tour with Michael Osman --maybe highlight the two major museums, and a couple of other places in the city, and then a nice dinner at night. Michael (once you reach him) could make the reservations for you. He would not be at dinner! He is a superb guide--he will tailor it entirely to what they want to do. He is pleasant to be with (more than that--fun to be with), and tells the history or art anecdotally.
And he is MOST reasonable.
I like the idea of LUNCH at the Eiffel Tower--it will take a good part of the middle of the day. It would also get them to the top easier, although you could also give them tickets to get to the top of the Tower, if they don't do lunch.

I agre with Gretchen Michael is a treasure and fun to be with. Hw will also go outside of Paris. We had him for a day in Giverney.

His "highlight tour" of the Orsay and Louvre were SO good. Not the biggies, but because he is an artist, at the Orsay he gave a sort of "continum" of the Impressionist movement, and at the Louvre showed us the structure of the chateau--so interesting. We had been to Paris MANY times, and that time, with our adult children, he showed us all things we hadn't seen before.