1. 1952
As we mentioned before, Princess Elizabeth became Queen Elizabeth in 1952 when her father, King George VI, passed away. She learned of her father's passing at Sagana Lodge, where she and Philip were staying in Kenya. They quickly ended their trip and returned to England, and then moved into Buckingham Palace. 

King George VI died in February, and here's the Queen with her children, Charles and Anne, at Balmoral Castle in Scotland, later that year. 

For reference, Charles was born in 1948, and Anne in 1950.