We took our kids to Disneyland Paris. They loved it. One of the best memories of their life. They weren't expecting it, we surprised them the day before, and had a wonderful wonderful day. (It was also much cheaper than DL or WDW)

But I have all girls and they love love Disney. We have 3, similar to the age of your two oldest, so there was no dealing with little kid issues. We all went on the same rides together, loved talking/hearing things in French (my oldest is taking French classes next year mainly because she had a great time at Disneyland Paris), they just loved it.

Other things we did in Paris that I would comment on:

Climb Eiffel Tower. You can go up the first two levels by the stairs. If that's within your physical capabilities, that's a fun adventure. Walking up the steps makes it more real than an elevator. We didn't even take the elevator up to the top, wait was too long and cost was too expensive.

Louvre - again, it depends on your kids. My kids loved loved the Louvre. I was really impressed at how much they liked it; I remember thinking oh wow, I guess my kids are old now because they like the art museum. (Your 3 y/o won't get a ton of enjoyment out of this...but that's ok, sometimes 3 year olds have to do things they don't like. Otherwise all your vacations will be just playgrounds and mcdonalds, right?) They liked seeing the Mona Lisa - it's famous to them too. I also had Rick Steves' guide to the Louvre and he gives just enough in his descriptions that I could describe what they were looking at and why the artist did this, why it looks similar to other things we've seen. My kids are artists, they draw all the time, so we had a sketchbook and they sketched some of the favorite things they saw. Last thing here - there's a YouTube series called "Great Art Explained" that we watched before of the things we were planning on seeing. Oh and kids are free at the Louvre which is nice.

Luxembourg Gardens - Beautiful gardens in the middle of the town. They have a big fountain/pond where you can rent little push boats (as well as watch some people with RC boats which is fun too)

We haven't made the Catacombs yet and I regret that. Some day.

Playgrounds / Carousels - Grand tradition in Paris of Carousels. There should be a carosel with views of the Eiffel Tower somewhere which makes for fun photos. My kids loved this playground in the middle of the Jardin des Tulieres west of the Louvre. A stop like that for an hour makes a big difference in their enjoyment of the day, and you can people watch which is fun.

My kids have watched a lot of the TV shows Ladybug and Cat Noir as well as Madeline, so anything that connected with those shows was a big hit for them.