The parent Plus loan is, I think, at 8.5% but it also has a 5% origination fee. You can start repaying immediately or ask for a deferment while your child is in school. I think the repayment can be up to 10 years, just like the student loans.
Private loans may have a lower interest rate, but the protections and terms will be different. You have to compare them and decide what is best for your family.