What is PEI???
We have traveled a lot with our (now) 4 year old boy, since he was 4 months old. For the car bring activities. These are some of our favorites:
magnadoodle (they make a small travel version)
Aquadoodle (also in travel fold-up version)
or any of
water-pen coloring books
(although if you have a baby maybe you want to skip this one unless the older two can keep it far away from her)
or just good old-fashioned pad and colored pencils
I also play children's CDs in the car for long drives
For the baby just bring some smaller toys. I usually buy a new toy or book just for the car/plane/boat and the novelty of that keeps him occupied for awhile.
And of course for everyone bring plenty of sippy cups and snacks. I usually have a separate bag just for snacks when we travel.
We have taken our kid on a ferry too, and the simple excitement of watching the cars get loaded in, and all the goings-on of a boat, plus looking at the ocean and islands was enough to keep him entertained.
Both of those trips sounds pretty short too, less than 2 hours. I think they'll be fine. Have fun!