We took our children to Paris twice. Once when they were 5 and 2, and once when they were 14 and 11. I think you will have a great time as long as you don't try to see too much each day.
Of your potential sites: My kids enjoyed going up in the Eiffel tower, the Seine River Cruise, and the Luxembourg Gardens. The Louvre was too much much when they were young.
Some things that worked for us that you may consider:
The Paris Metro is fun. I would take that instead of a hop on hop off bus.
Renting an apartment is nice and lets you have a refuge for preparing some of your meals and doing a load of laundry.
The Orangerie museum (
https://www.musee-orangerie.fr/en) was an unexpected family favorite. It has huge Monet water lillies paintings, and other art from artists that you will have heard of. But by far the best part is that it is so much less famous than the other art museums in Paris, that it is much less crowded and therefore much more enjoyable.
The Luxembourg gardens (and other big parks in the city) may be wonderful, especially for your 5 year old. Some of the parks (sorry, can't remember which ones) have big climbing structures (much higher than US playgrounds) that our children loved. And some of the parks have sets of outdoor trampolines or merry-go-rounds with brass rings for the kids to grab. If more than one adult is going, I would recommend maybe one touristy activity as a family in the morning, and then the adults alternate days taking the 5 year old to a park in the afternoons, or seeing other sites with the 15 year old, and then come back together as a family in the evenings.
When you visit Versailles, consider seeing the grounds first, and maybe renting tandem bicycles from the bike rental place on the grounds. The line for the palace tour was much shorter in the afternoon.
My other recommendations are to let each kid pick out some of the activities and don't cheap out on on cold drinks, ice cream cones, and crepes when out sightseeing.
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