Here's a great article on the problems that it can cause.
http://finance.yahoo.com/news/student-loans-almost-ruined-relationship-110037139.html
If for some reason you have already done this. Make sure you take out a cheap term life insurance policy on your child. The only thing worse than your child not paying them is not being able to pay the student loan because he or she died! Make sure to get enough life insurance to pay off ALL of the student loan.