The flight response is when they try to disappear and fade into the background when there's a challenge which might work if there's a fight going on and they want to escape but isn't ideal if they're being bullied in the playground or if they need to give a presentation at school.
Freeze is when they just go still and quiet, neither fleeing or fighting and this can be useful as a chance to stop and consider how to respond but isn't fast enough if they're needing to protect themselves.
So first find out how your child naturally responds. Be curious and watch for patterns in both actions and words. Then discuss with them what a better response might be in that situation. Practice at home. If your child is complaining of their sibling attacking them and they are coming to you to sort it out, ask them what they could do themselves that would be a good strategy.
If they are answering you back, ask them whether they think this is the most sensible response. What would be better? Check with them what outcome they want and ask them to think about what behaviour might result in that outcome. Children are so 'in the moment' which is great for play but not great for strategic thinking. For that, they need to project forward in time just slightly and think about what they'd like to happen. Then they can weigh up possible options.
Mindfulness practice is a good way to learn how to respond to external events in life and many children are learning this at school.
Another way to improve your child's resilience is to introduce them to being more internally referenced so that instead of judging themselves purely by how others respond to them, they have some insight into their own judging and values so they have an internal self-esteem which reminds them that the other person's opinion is only that, it is not a fact.
Lastly, point out when you notice your child being resilient because when they know what it is, it's easier for them to be it. So for example when they tell you that someone at school teased them about something you know they are sensitive about and they tell you they didn't respond then you might remark 'that shows great resilience' so they know and can add it to their skills. This builds self esteem.
Judy is the author of 'Confidence for Kids' for your download get her free app NLP Family. Judy offers a four session Confidence and Resilience course for children and young people either on Skype or Face to Face.