No extra charge for the baby seats on the bikes.
Yes you can walk anywhere you can ride on the island. We walk over to the airstrip and down it to the adult beach every time we go. That is where the bike/ walking trail is too. We walk to the end of it and back to the family beach. We rented the bikes our first time to CC for an hour. It was fun to do a family ride together, an hour is more than enough time to ride over all of the island that your aloud to go to. Now we just walk it instead of renting the bikes. It is a fairly long walk to take, but you can catch the tram at the adult beach and take it back to the main part of the island if you dont want to walk all the way.
I guess each family would have to decide if renting the bikes are worth it. It is faster with bikes, but we enjoy stopping and getting up close with some of the beautiful foilage they have on the island. On a bike we would of just went past it. You dont have to reserve bikes ahead of time, just walk right up and do it on CC. That way you can walk around a bit and judge for yourself if it's worth it to you. They do have water stations in several places so you can get cold water wheather your walking or biking.
mom x4,grandma x4