Paris with a teen - Jardin de la Menagerie in Seaux or La Defense

What time is "afterwards"? Neither of these location are in Paris but from Seaux, you could take the RER B into Paris, have dinner somewhere near métro 1/RER A, then proceed to the hotel after.

The concert is from 6pm to 7pm. so after the concert ends

So I looked at the RER routes. Is it all underground? is there a scenic way to travel from Seaux to La Defense. Some routes look iconic on the map, but is it that way in reality?

La Defense is a soulless office park. I would agree with those who suggest going into Paris for dinner and then taking the RER back to la Defense and the hotel. If you wanted the classic boeuf Burguignon and the best grand marnier souffle around then you could eat at Chez Dumonet, Josephine and take the 13 to the 1 and the 1 metro to la Defense.

Seaux is a long way from la Defense and the way back is through Paris anyway -- you would take the RER B to Paris and then transfer to the RER A to la Defense. Perhaps someone has ideas for restaurant near this connection in Paris.

The RER tends to be underground in Paris and above ground outside Paris but none of it is scenic. The outskirts/suburbs are not very attractive from the train tracks.

My son raved about La Petite Pergourdine https://www.restaurantlapetiteperigourdine.com/en/. It serves southwest French style food, a style of cooking our family likes a lot. He said it was the best meal he had when he was here in France a couple of months ago.

To get there: take the RER B from Sceaux to the Saint Michel stop for the Petite Pergourdine. After eating, to get to La Defense take the Metro 1 to La Defense.
The easiest is to return to the Saint Michel stop, take Metro 4 direction Porte de Clignancourt for two stops. Change to Metro 1 at Chatelet. This is a very easy change to do. Take Metro 1 to La Defense.

You can do the exact same route by RER, changing from RER B to RER A at Chatelet, but the RER requires descending much further underground.

Book a table at
Brasserie des Arts about a 5 minute walk from the RER B station at St. Michel Notre Dame.

Definitely do not eat dinner at La Defense. It is an office area like anywhere else in the world, Paris has so many wonderful restaurants.

While there are no restaurants of note in La Défense proper, there are some good options in Puteaux, such as l'Andouille.

But for performance day, it makes sense to eat somewhere between Sceaux and La Défense: this means Paris, anywhere along RER B and RER A or metro line 1...that's a lot of options. Of note for a teenager, maybe: there is a high concentration of good Japanese restaurants just west of the Palais Royal, around rue Sainte Anne. Hakata Choten or Kodawari Ramen, for example. The main downside is that the lines can be very long.