The 18th birthday party for any individual is a very important one. This is the day when a person moves from being a child to an adult. The United Nations recognizes any person below the age of 18 as being a child. To attain adulthood and to be able to make independent decisions you have to be at least 18. This is the law in several countries. After 18, you can get married and you are free of guardianship. Hence, the 18th birthday is a very important one for most people.