You can also do part points and part cash. Some people use points for the adults and pay cash for the kids. Or you can use points for one adult and pay for the other.
I think a lot has to do with how much extra money you have to spend and if you are planning to use points for other things that year.
We were going to use points for a cruise next year, but ended up booking with cash. But may use points for the following year's cruise.
DJ