Yes is the simple answer.
Here's the more complicated version...
There is not a baby swap for any ride without a height restriction. I.e., if there is no height restriction, any child can ride, including infants. So, a baby swap option is not offered.
For rides with a baby swap, you can take up to four (or five? I can't remember) with you. So, your DH, DD, and DS could ride while you wait with the baby, and then you could ride with DD and DS while your DH waits with the baby. So, your DD and DS will get to ride some rides twice (my older DD loved this!).
In reality, if your baby can't ride due to height restrictions, unless your DS is really tall for his age, he probably won't be able to ride either.
Here is a handy height requirement calculator - with your kids' heights, you can see what they can and can't ride...
http://www.wdwinfo.com/wdwinfo/height.htm
Here is more info on the child swap...
http://www.wdwinfo.com/childswap.htm
http://allears.net/pl/infant.htm#toosmall
Have a great trip!