This is where living in the Vallée de Chevreuse is an advantage: these outings feel distinctly French without spending half the day in transport.
Large grounds, a real château, Perrault fairy-tale scenes, maze/gardens and enough freedom that the children are not being told to whisper for three hours. During Paris school holidays, a storyteller is scheduled daily at 16:30.
A 130-hectare wildlife forest rather than a conventional zoo: deer and other animals in wooded spaces, wolves, free-flight raptors, play areas and giant suspended trampolines. Summer holiday hours are currently 09:30–19:00.
A medieval castle above Chevreuse that works when nobody wants another “big attraction”. Walk the ramparts/viewpoints, then descend into town for a crêpe or ice cream.
Île-de-France gets a very deep partial eclipse, around 92%. Regional calculations put the beginning around 19:22, maximum around 20:17 and the end around 21:10. Because the Sun will be low in the west, choose a place with a completely open western horizon rather than a wooded valley.
Make it an outing: early picnic, cold drinks, a field/viewpoint with a west-facing horizon, certified eclipse glasses for everyone, then stay for sunset. Regular sunglasses are not safe for direct solar viewing.
For Canadian visitors, the surprise is often not “nature” itself but how quickly a French village, abbey, forest and boulangerie can fit into one small radius. Keep this as a low-energy option during the heat.
Instead of an attraction: castle viewpoint, old streets, the Yvette, a crêperie. It is the sort of half-day that shows them how you actually live here.