Getting around Paris

As Courbevoie is not in Paris, I assume you will be using the RER A/métro a good bit. There is a zone 1-5, day pass at 12€ that includes all modes of public transportation, i.e. bus, métro, RER, Transilien trains, funicular, and tramway. This day pass excludes airport access. Otherwise, individual tickets for the métro/RER/Transilien trains are 2.50€; bus/tramway tickets are 2€. Individual tickets are available at half price for children 4 to 9.

Either of these options, tickets or passes, may be loaded onto a Navigo Easy card (2€), or onto a smartphone using the Ile de France Mobilités app or the Bonjour RATP app. Each passenger must have his own card/app.

Children under four ride for free and those four to 9 pay half fare so your teens are not eligible for discounted fares. It does not matter how young they look.

your kids are free for museums and get reduced fares for the Eiffel Tower but not for transport. Be sure to book any museums you want to visit well ahead as major ones do sell out a few days ahead.

I assume you are staying in the boonies because you are driving and the hotel has parking, otherwise for such a short trip that is a huge time sink in commuting.

Thank you
I have no idea what 'boonies' are but the apartment is in La Defense and says it is 15 minutes out, so not a huge amount of time. It is the right side of Paris for Montmatre, Eiffel Tower etc.
We won't be doing any museums - just spending the day (and maybe the afternoon before) walking about and sightseeing
I will get the app loaded onto our phones then, thank you for the info

suepeta, “Boonies” is a figure of speech, short for boondocks. Essentially meaning you aren’t staying in central Paris but a more remote area.

the apartment is in La Defense and says it is 15 minutes out,

Are your accommodations in Courbevoie or la Défense? If you are in la Défense and a few minutes walk from the RER A station, the ride to an RER station in Paris will take about 15 minutes. The RER A does not go to Courbevoie, you´ll need to connect to one of the nearby RER stations via bus or maybe Transilien L. To return in the evening, you might be dependent upon evening bus schedules which may be limiting.

For example, from bus 178 in Courbevoie (assuming you are somewhere near the bus line), and making the required connections to reach Sacre Cœur (Montmartre), plan on over an hour. Please confirm this information and take a look at any of the route planners such as Citymapper, IDF Mobilités, or Bonjour RATP.

Sometimes the devil is in the details. Allow time to reach any location in Paris and to return to your accommodations.

A couple recommendations:

1) We found it easiest to use our phones to buy metro/train and bus passes. There are two methods that we used. The first is buying them within the Apple Wallet app on our iPhones -- insturctions here https://support.apple.com/en-us/118581. The second is buying them within the Bonjour RATP app. I recommend purchasing them in advance when you have a strong internet connection, and not when you're within the underground metro system.

If not everyone has a phone on the trip, you can use the Bonjour RATP app still. One way is by adding tickets to an Apple Watch if someone has that -- their phone will be one metro pass and their watch a second pass. Another method is to buy a physical Navigo Easy card at one of the machines in a train station. Then, using the Bonjour RATP app you can still refill that physical card as needed without going to a machine in the station.

2) I would use the Bonjour RATP app for navigating public transport options when you're going from point a to point b, and not apps like Google/Apple Maps. We experienced a couple times that Google Maps was not aware of cancelled trains, while Bonjour RATP was.