Welcome Aboard, Mark!
First of all, you will definitely NOT be the only family with a young baby onboard your Disney Wonder cruise! You might consider booking some time in the "It's a Small World" Nursery for your little one, so that the adults can enjoy some alone time...maybe a visit to the
Vista Spa & Salon for a massage?
You are right is saying that your 4-year old will have a blast. The
Oceaneer Club and Oceaneer Lab will keep him occupied for hours on end. I'm sure he will also have a ton of fun splashing in the pools and going down the Mickey's Pool Slide.
Be sure you bring an infant carrier to save your arms while you are wandering around the cruise ship. Also, a small umbrella stroller to take on any Port Adventures, which can be folded and slid under the bed for storage. Some other fun tips for cruising with little ones can be found
here.
Thank you for visiting the Disney Parks Moms Panel with your questions about your vacation on the Disney Wonder. Please come back with more questions that arise before you set sail!
Happy Cruising, Tracy V.