I was there a number of years ago and I took a tour from Paris. The bus was full, my knees were in my face the whole trip there and back. We spent a couple hours there and yes the flowers are beautiful, God does good work. NONE of his paintings are there, just cheap copies in the souvenior shop. You can see some of his paintings back in Paris. The lily pond is nice, but with hundreds of tourist walking the paths it loses its charm. His flower gardens are planted in rows like a vegetable garden, but the purpose to Monet was to study the plants in different light conditions. There are a number of beautiful gardens in Paris I would prefer. His house was drab to say the best. I guess I could not figure how a man who could paint so well, could live in it. Some people are crazy about, but maybe they are crazy also. Take a look at this and you decide if you want to take a day out your life to see it. http://giverny.org/gardens/fcm/visitgb.htm
If you rent a car maybe as a detour to see other places on the way or in the area.
This is just my opinion, but I will tell you I could not wait to get off that bus. And with children that age, definitely not.
There are some beautiful gardens/parks in Paris your children may enjoy, areas in the Luxembourg Gardens being one.