You can take your baby with you on any ride for which there is no height requirement.
If you look at this page of travel tips for people with small children found
HERE,
you
will see a button on the right hand side of the page that says
"Height Requirements." Clicking on this link will bring you to handy PDF that you can download. The PDF lists the attractions in all four
theme parks and both water parks that have height requirements. If an
attraction is not listed on this document it means that there is no
height requirement and any age/size child can enjoy the ride. As you can see, some of the rides that anyone (including babies) can enjoy are: Small World, Pirates of the Caribbean, Jungle Cruise, Dumbo, Winnie the Pooh, Buzz Lightyear, and many, many more.
Unless
your older children are exceptionally tall, my guess is that there will
be very few rides that they can go on that your baby can't.
Have a great vacation with your family!