OSNABRÜCK, GERMANY — Playgrounds can tell you a lot about a society.

I used to cycle to work through the Square des Batignolles, our local park in western Paris, and was always struck by the almost uniform ethnic segregation: mostly white toddlers chasing each other and their caregivers, brightly clad West African women chatting away on the benches rimming the sandpit. On those same benches on Sunday afternoons, I would socialize with other young, professional French mothers.

Here in Germany, the only adults populating playgrounds on any day of the week appeared to be mothers — often mothers with a university education who not long ago earned a respectable income.

Of the several social insights to be gleaned from this comparison, one is surely this: French mothers work, and many of them full-time.

The nanny culture seen in Paris is by no means unique. Indeed, in places like New York City and London, where the system of state child care is generally less developed than in France, nannies are also a common sight.