Can anyone give legal custody of there kids to anyone. Not adoption. Just give temporary or permanent custody by just signing some papers? My sister let my 16 year old nephew go live with an old neighbor in another state Florida. My sister lives in California.
No you cannot do that, you need a court order.
Sometimes a parent will sign a Special Power of Attorney giving someone short term ability to care for the child.
Need a whole lot more info. Is there a relationship issue between the old neighbor and the nephew. Did the nephew attend high school and wants to finish school there? Did your sister give maybe a Special Power of Attorney or temporary guardianship to this neighbor.