Paris Catacombs

http://mylittlenomads.com/paris-for-kids
This is a great attraction for understanding the history of Paris. In the late 18th century the cemeteries were a breeding ground for disease and illness. The graves were emptied and the bodies stored underneath the city in the Catacombs. There are 6 million skulls and skeletons – victims of the plague, the French Revolution and the guillotine. It isn’t as ghoulish as it sounds and most kids are not scared by the sight. My big warning here is the wait which can be anywhere from 1 hour to 4 so get here early and have some snacks (there is a McDonalds and a grocery store nearby if the kids are hungry – one parent can stay in line).

http://www.catacombes.paris.fr/en/homepage-catacombs-official-website 
Tour Montparnasse 1.4 km 

http://www.catacombes.paris.fr/en/visit/access-opening-times-accessibility/museum-admission
pilet 10, audioguide 3 eur
Open daily from 10am to 8pm, except Mondays and public holidays.
Métro et RER B : Denfert-Rochereau