Famous only children

According to the website www.onlychild.com,these are famous only children.:
The list:
1.Comedian Robin Williams
2.Natalie Portman
3.Rudy Giuliani
4.Tipper Gore
5.Lillian Hellman
6.Kareem-Abdul Jabbar
7.US president Franklin Delano Roosevelt
8.Treasurer Alan Greenspan
9.Actor Cary Grant(1904-1986)
10.Frank Sinatra
11.Ada Byron
12.Cole Porter.

In addition to these 12 people,these two people were also only children
1.Actor William Powell(1892-1984)
2.Silent film actress Elsie Ferguson(1883-1961)