It’s very doable in brookline. Dr office and dentist office are on beacon so walks to the pediatrician or dentist are easy. You want to get a decent stroller, there is a reason everyone has citi minis and uppa bay vista. The bigger wheels and suspensions make the ride a lot easier (also handle snow). Get a rain cover they are good for windy days too. Also get war muffs for your hands and something like a bundle me.

If you are still young enough for the baby bucket seat, you can get adapters for everything.

The second car on the green line are the lower ones so longer trips are a hop on the train. It’s usually filled with people with strollers in the flat well there

The car seat carrying caddy type strollers are basically shopping carts and can hold a few bags underneath for groceries . I actually miss that