Dreams involving demons and the act of saving loved ones can be quite intense and may reflect deeper feelings and concerns in your waking life. Here are some possible interpretations of your dream:

1. Fear and Protection: The demon may symbolize a fear or anxiety that you feel is threatening your family. Your instinct to save your children indicates a strong protective nature and perhaps an awareness of the challenges or dangers they may face.
2. Family Dynamics: The setting of your grandmother's house could represent your childhood or family history. This place might evoke feelings of nostalgia, security, or unresolved issues from your past. The act of saving your daughter but struggling with your son could point to feelings of favoritism, guilt, or concern about their different needs or personalities.
3. Transformation: The moment your son’s face changed might signify a fear of change or loss of connection. It could represent your worries about how he’s growing up or the potential for him to face challenges that could alter his personality or behavior.
4. Emotional Conflict: The dream may also highlight an internal conflict you’re experiencing, possibly related to parenting or your own fears and insecurities. It could be a reflection of your anxiety about not being able to protect your children from harm.

To gain further insight, consider reflecting on your current life situation, your relationship with your children, and any recent events that might have triggered these feelings. It may be helpful to talk to someone about your concerns if they continue to weigh on your mind.