Self defense for your child

Scenario: your 11 year old is packing their things from the end of the school day after the bell rings. They know they have to hurry and take a different route home because the same group of kids has been picking on them and your child wants to avoid the situation. As your child exits the building he sees the group still waiting, the child goes back inside and asks if he/she can call you. He/she calls and it goes to voicemail. Being scared to tell the office why he/she won't leave, he/she decides to tough it out. As he/she exits the building again the group is there waiting but your child avoids eye contact but the group stays a few feet behind. After they're off school property, your child gets circled and shoved. 
From there on, do you believe your child should fight back to get out of the situation? Do you think they should just block punches coming at them but not throw a punch? Or use foot work to try and run but they could already be injured and can't get away?
I'll be putting my children in self defense classes to learn the correct times to use self defense. 
If you don't teach them the skills they won't have a shot with even 1 person (that's my outlook and they will have discipline in a class) Children don't always tell adults, that's the point I'm trying to make. Out of fear. =\