"Just ignore it."
A child is coming to you for help because they probably tried that already and it didn't work. The message this might send is that YOU don't want to take the time to help them through this. What if things get worse and your child thinks you won't help them, so they decide not to ask for help again? Never tell a child to "just ignore it" if they're being bullied. IT DOES NOT WORK.
"Don't be so sensitive."
Way to go, you just invalidated your child's hurt feelings! No, don't ever, EVER say this. Again, this pushes the child away and they might decide you aren't the person to come to when they're hurt or upset. It's dangerous, especially if they're suffering from depression due to the bullying. Don't say it, no matter how badly you want to. Some children are more sensitive than others.
"Don't take it so personally."
Suppose a bully walked up to your child and said, "(Child's name), you suck at life. You're worthless, useless and you don't deserve to exist. You're ugly and everybody hates you. I hope you kill yourself, you piece of sh*t." That sounds like a pretty personal attack to me. What if the child's locker was vandalized, or they had textbooks, their backpack or other valuables stolen by bullies? And you tell them not to take that personally? No. It IS personal, and saying this will shut your child down from asking for help.
"Well, what did YOU do to cause these kids to start teasing you?"
NO! NO, NO, NO! Never say this! NEVER! I mean NEVER! This is the ultimate act of victim blaming and it will hurt your child for the rest of their life. This will guarantee your child believes they deserve it and they won't ever come to you again. This is the statement my father made that led me to believe I deserved the bullying I got. I never did ANYTHING to ANYONE. I was too short, too underdeveloped and too different from my peers to fit in. This statement is what made me stop reporting the horrible things other kids did to me. I suffered awful things in silence, and I still don't know how I'm alive today. This is THE WORST thing you can say to a bullied child. DO NOT SAY THIS!
What CAN you say? What SHOULD you say? I can't tell you the exact words to say to a bullied child. The first thing you should do is let them talk to you. Just listen. Don't try to fix it, don't interrupt, just listen and let them tell you everything. It may be the child just wants to be heard.
The worst thing about being bullied was feeling like no one cared or wanted to hear me. Don't do that to your child.