A good public transport system is not difficult for families and even easier. Berlin has a pretty good public transport. We had a car when we first moved here (we're a family) but we never had the need to use it other than 1-2 occasions in a year because public transport + biking is easier, faster and more comfortable.
At the end we got rid of our car and not planning to buy another one. For those occasions that happens 1-2 times a year, we just use a car sharing app. It's also a lot cheaper than maintaining a car.
Sadly, Paris is not that. It's a great public transport system without families, but not for anyone with young children or with mobility problems. I can make do, but only if I have my 18 mos. old in the stroller OR my 3 year old walking, but not both. (It's a bit easier for my wife, because people will stop and help her up and down the stairs with the stroller.)
Buses do tend to be a bit easier if you're travelling outside of peak hours. Otherwise, you might have to let a bus or two pass you before one comes with enough space for the stroller.
Things are supposed to be a lot better with the Grand Paris Express, although that won't help much intramuros.
At the end we got rid of our car and not planning to buy another one. For those occasions that happens 1-2 times a year, we just use a car sharing app. It's also a lot cheaper than maintaining a car.