We are going to spend a week in Denmark at the end of August, half of the time in Copenhagen, half on the island of Aero. We will have our 18 month old son and my adult brother with us. We would like to avoid renting a car if possible. How easy is it to travel by train/ferry from Copenhagen to Aero? How easy is it to get around on Aero without a car? Remember, we have a toddler in tow. Thanks very much!
I think any of the towns in Ærø, like Ærøskøbing, are small enough to get around just by walking. Rick recommends getting around by bike. http://www.ricksteves.com/plan/destinations/scan/aero.htm When I was in Denmark, I saw plenty of bikes with attached buggies for kids to ride in, so I bet you could rent something like that.
For the Copenhagen part of your week a 72 hour Copenhagen Card gives you transportation for all of Northern Zealund including bus, metro and trains. The card will get you as far west as Roskilde, south at least to Dragor, and north to the castles and beaches. It also includes free admission to a variety of places.
I haven't seen the best deal for Aero yet so can't comment.
My first recommendation for toddlers is grandma's house. If you can't (or don't want to) take my first suggestion, my second recommendation is a basic umbrella stroller. It folds up relatively small and is easy to carry when you need to (stairs).