A few tips you may think about
1)Asking him/her directly: They are children, but they can answer back to a simple question such as «How are you?» or «How are you doing?».
2)Exploring temperament: When talking with children and parents we may ask about their usual way of behaving? Are they more phlegmatic or impulsive? How they react to an unexpected stressor?
3)Exploring usual coping strategies: Moreover, we may ask about what usually helps them coping with stress: «Which are their usual strategies?».