Be My Friend - S4.E17

When Laura is playing along a creek, she finds a bottle with a note in it. The note read, ""Be my friend."" Laura convinces Pa to help her look for the person who sent the note. They end up finding a baby. Charles then searches for the parents of the child. The baby belongs to teen parents. The reason the mother left the baby for the Ingalls to find was because her dad was opposed to her being with the guy she conceived the child with. The young parents take the baby and try things again.