The youngest will always be the baby. Each position is totally different and influences that child's behavior. Each child must find his own special place of significance in the family. They must compete for their parents' love and attention. Insecurity can result when a child has not felt loved and valued unconditionally.
Most sibling rivalry is an attempt to boost the child's position in the family.
Tattling, for example, places the tattletale in a superior position. He is trying to make himself look good in the parents' eyes, and make the sibling look bad. Therefore, it is better to ignore tattling in most cases. There is plenty of competition in school, in sports, and elsewhere. Try to decrease the competition at home.