Looking at buying an XC90, have kids aged 7,6,2,0 also have a boat etc?

Whats the turning circle like?

The XC90 should work great for your family and towing that boat.They have come a long way in the past couple of years.

You didn't say how heavy your boat trailer is...I'll comment 'in general':

Be sure to get the Volvo-brand towing equipment (don't go to some aftermarket brand of hitch), and be sure to confirm that your boat trailer's maximum weight (boat, with all fuel and equipment) and tongue weight are within the maximums of the XC90's ratings -- also be sure that you have trailer brakes, if required by the XC90's criteria, as well as by your state's statutes. Exceeding these figures will nullify your insurance coverage and leave you liable for a traffic citation if your stopped and checked, not to mention culpable in an accident.

Also the information poped up recently that the towing capacity on teh XC90 has been lowered so be careful when towing anything with it unless you know it is within specs.