Have them put on the meter (2.50 EUR flag fall, iirc,) and worry more about delaying traffic...
We are 2 adults and a 4 yrs old. Should we reserve the van or shuttle or not much different if we go with a taxi when we come out the ORY (convenient for us not to book)?
In 2008, there were 4 of us/adults plus 1 child who took a taxi from CDG. The price was around 50 Euro which I thought was about right and reasonable. I don't know how common to have a taxi that would cheat ...