France - 1 Day Itinerary

By "a day trip" do you mean you will have one full day in Paris (as in, sleeping overnight in Paris the night before and the night after)? Because that's how much time you'll need if you take in all the sights you have listed. The Louvre alone could easily take an entire day if you want enough time to appreciate what you're seeing.

Yes, hop-on-hop-off bus is a handy way to see the main sights of Paris (or any major tourist destination city) in one all-inclusive price.

If you're traveling to/from Paris on the same day, with the Netherlands as your base, even if you get an early start you'll have only a few hours in Paris before it's time to return. For example, by train from Amsterdam you're looking at more than 3 hrs each way, not counting getting to the station etc. If you flew it would be faster in the air, but airport security etc. would balance out to be about the same as the train.

Don't know where you are coming from in the Netherlands, but even from Rotterdam, its a 2 3/4 hour trip each way on the fairly expensive Thalys train. That maybe gives you maybe 8 hours in Paris. Louvre eats up a lot of time, 3 hours even for a cursory visit, so maybe skip and hit a few spots. Get reservations for the Eiffel Tower on their website so you don't spend much of your limited time sanding in line. Seine cruises go very frequently from several locations, one by the Eiffel Tower. Hop on/Hop off buses are an option. one route makes a stop by Gare du Nord where you arrive from Netherlands. There is also a Hop on/Hop off boat route on the river. You can also get around easily on the Metro.

It is possible. There is a 6.25 high-speed Thalys service, getting you at the Gare du Nord at 9.42; the 19.25 is the last day train to get you back, also taking some 3h15.
It does give you the opportunity to see a couple of highlights and to taste a little bit of the atmosphere by having a good lunch, but not really for time-consuming activities such as a boat trip or a museum visit. Paris is a compact city. Most of the highlights - from Eiffel Tower to the Notre Dame - can be done on foot, starting with the metro station Charles de Gaulle-Etoile and finishing at the Bastille station. It will be a long day though, and it won't come cheap, even with advance booking. Check for the ticket prices at the Thalys website.

Personal bias -- the few times I have used a hop-on hop-off bus, I did not hop off once, since I wanted to get the complete overview of the city. HOHO seems like an inefficient transportation mode to me -- easier to determine my priority sights and just get to them only, not drive by stuff somebody else wants to see (and waiting for the other passengers to disembark/load on.) If you really want to see all those places, maybe taking taxis would be cheaper than four HOHO bus tickets.

We had planned on taking the train, but as you responded it seems quite expensive. We are coming for the Sittard area in the Netherlands. We are renting a car for our time here, so maybe best to just make the drive from Sittard to Paris ourselves? Since it seems as though we can't see/do everything in my original itinerary I think it may be best to spend the night in Paris. Any suggestions on a place to stay with 2 kids under the age of 10, for a night? I apologize in advance for my questions and if I am missing details. I have only travelled abroad once with the military so all of this is new to me. My husband has travelled to the Netherlands many times to visit his family but the last visit was 30 years ago. I figure if I'm this close to Paris, I have to visit.

How thoroughly do you want to see each of your sites? "Seeing" the Eiffel Tower doesn't take long at all, if you mean you just want to go there and look up at it and take some pictures. But if you want the full experience of going up to the top, that takes a lot longer. Similarly, the Louvre is huge, and seeing the whole thing would take ages, but if there's just one particular part of it you're interested in (the Mona Lisa, maybe?), that can be done much more quickly.

A hop-on-hop-off bus can be a good way to get your bearings and get a glimpse of the main sites, but I wouldn't plan on using it as your main transportation all day. A Metro day pass is better for that. It doesn't cost much.

Traveling by car might save money (assuming you can finesse the parking situation in Paris), but it probably will cost you time. ViaMichelin estimates 4 hr. 21 min. from Sittard to Paris, and folks here seem to consider VM optimistic.

We will be there from 4/26-5/3. Half in Netherlands and half in Paris (and a day in Brussels).

When you plan your Paris day, don't go on Monday(s) and know that May 1 is a major holiday (which also happens to be a Monday).

I would agree with most that a train in and train out same day will give you very limited time.

I also found that it was cheaper to buy tickets on the NS website. It was cheaper than both raileurope and sncf app (though on the sncf app, I was able to select my seats which I could not do on NS)