Besides the big things like getting hurt, kidnapped, molested, etc.
1. That they will be bullied (or become a bully).
2. That they will turn to alcohol and/or drugs in their teens.
3. That they will marry someone who thinks I'm a horrible MIL and tries to separate me from my kids and grand kids. This was never really a fear until I got on DS and realized many women hate their MILs.
Amanda - happily married wife to N
and mother to B