I just found out today that my plan for LO's birthday is not possible. We were going to have a small grandparent party and then bring him somewhere but the place is not going to be open so back the drawing board!

What do you think would be the best option - in or around Boston in early May?

1. Zoo (we have membership and go quite often to our local zoo but we can go to the much larger one in the city instead)
2. Children's museum
3. Aquarium
4. Daytrip around the city (take train to/from, ride swan boats or duck boats, see all the big buildings and food trucks, etc.)
5. Birthday party at home with friends

Older brother will obviously be going with us and he is 3.5. We have never taken either of them to the museum or aquarium and they've never ridden the train into the city but have been on a train ride before. We have been to the zoo and walked around the city several times. We will still have a small grandparent party regardless and if we invited friends it would just be a small group that we see all the time.
Now that I've written a book, which option would you choose or do you have a better suggestion?