Parents need to teach their children that God will always give them the graces that they need to carry whatever cross is handed to them. Parents should also teach their children to find something positive about every cross. Sometimes the only positives that you may find about a cross is that you can earn graces, comfort Our Lord and save souls by offering it to Him, but those are huge in the scope of life, aren't they?
As for bullies, if your kids are in danger, you need to step in and keep them safe. If they are not in danger, teach them to do as Our Lord would: Turn the other cheek, treat others with kindness. I have helped my kids over the years with a few good comebacks, but usually I'd tell them to just avoid the person taunting them, or do their best to treat the kid with kindness.