Sweden has one of the best public transportation networks in the world! All buses, trains, streetcars and subway stations are also wheelchair or stroller accessible, and one parent per stroller can actually ride regular transit buses in Stockholm for free! (Strollers board in the back, and it is not necessary to leave your child to try to pay.) Stockholm's subway system is also elevator accessible, and has 100 stations!
In many cities you will also find that your subway pass will also work on short boat/ferry rides from island to island. You can load up your pass at an automated kiosk (you can use your credit card) or at manned booths. Since each of the main cities (Stockholm, Gothenburg and Malmö) have such extensive public transportation systems, we highly recommend it as an efficient and reliable way to travel!