I have two kids (now 8 and 4 years old). I don't own a car. We never had any issue bringing them with us in public transport (bus, metro or train). We live in Barcelona.
Well there are six stores (from very small to a supermarket) within five minutes of walking from my apartment. There’s a gym 500 meters away and another 1 km away. Cinema is 10 minutes by metro. A huge park and a forest are also about 10 minutes away each. Density is convenient!