David I wouldn't skip the gardens at Versailles,, the boys can rent bikes there by the 1/2 hour and burn some energy riding around the canal,, its safe to do on their own,, my 14 yr old did it by himself while I took a break at the cafe right by the bike rental place. And for most younger folks they enjoy seeing Marie Antionettes estate, hopefuly they know the history behind that,, makes it more interesting. Instead of waterpark suggest you and boys take a Fat Tire Bike Tour,, they are easy and fun for anyone,, great way to see a bit of alot in Paris, you don't need to prebook either, ( except for the all day out trips) ,, I think the Night Tour is the best one,, you get a cruise on the Seine included.. the kids will enjoy it, the tour guides are younger and make it all fun. You literally just show up at the south foot of the Eiffel Tower at seven pm( as I recall, check their website to confirm) , eat before as they only stop for ice cream,, its a great way to spend an evening in Paris ,, kids don't want to go to bed at 9,, and even museums close by 9 or 930,, and seeing a show like moulin rouge is EXPENSIVE and not very good( in my opinion). They also do Segeway tours, but those cost more. As for bike tour( again, i know, but they are fun and kids will really enjoy them) please do not hesitate based on any fears of it being "hard".. its not, the first time I did one I hadn't even been on a bike in over 25 years,, and Paris is pretty flat.