Final answer:
Stuart's parents' kind behavior is evident through their warm welcome, invitation to supper, and genuine concern for their children's wellbeing and happiness.
Step-by-step explanation:
An example of how you could tell that Stuart's parents were kind people is from the given passage where the parents welcome their children home happily and invite them to join them for supper. This shows their kindness towards their children by being warm and inviting. Additionally, the fact that Stuart's parents ask about their children's trip and what they had to eat indicates that they genuinely care about their children's well-being and happiness. The parents' affectionate behavior towards their children is a clear indication of their kindness.