My kids that age LOVED the louvre. They still talk about it.
Traveling with young kids is an investment - we've reaped the benefits of them going when they're super young, now they know the drill and what to do.
You do have to bend the itinerary to their interests. We have more beach time and less cathedral time than I would otherwise. My kids love art so they like art museums. Old churches? Not so much, unless there's pictures and art in there. Things like that.
Travel has brought our family together and gave us experiences that we'll have forever.
Love to see that so many CB agree with this mindset.