In parenting, there are often more answers than questions.
Many parents have similar questions about their childrens' development, behaviors, mood, relational skills, etc. "Are toddler tantrums normal?" "How can I handle my child's aggression?" "Why is my child so shy?" "I'm worried that my teen doesn't have many friends."
Because every child has a unique personality, temperament, and experiences and families have their own dynamics and histories, the answers to these questions will depend on a variety of factors. One child's aggression may be the result of jealously of a new sibling while another's may be because of illness or fear. Each would be dealt with in a different way.
It's important to remember not to compare children but to consider their unique characteristics and the circumstances when trying to understand and deal with issues that arise. There's far too much comparison in parenting and this tends to just add to parental stress and worry and take away from the emotional energy needed to support children.