Yes | No Thank you! The average height for a 3 year old (newly 3 so 36 months) is 37 inches (CDC growth chart.) The average height for a 3 /12 year old is about 38 inches. Your daughter for her age is about the 95th percentile and 42 inches is average for a 5 year old.posted 07/20/2011 by puzzler.Report answer.he average height for a 3 year old (newly 3 so 36 months) is 37 inches (CDC growth chart.) The average height for a 3 /12 year old is about 38 inches. Your daughter for her age is about the 95th percentile and 42 inches is average for a 5 year old. posted 07/20/2011 by puzzler. Report answer.