A father brings his 15-month-old son to the well-baby clinic for a routine checkup. The father confides to the nurse that he is concerned that his son still crawls and does not walk. Which of the following responses, if made by the nurse to the father, is BEST?
1. "I will refer you to a pediatric specialist if he doesn't start walking soon."
2. "Have you noticed any signs of paralysis or weakness in your son?"
3. "Try standing him on his feet several times a day."
4. "Children frequently set their own pace for development."