I added my nephew and two nieces to my Hilton Amex to help them establish credit history. (Could not add my own children on AMEX since none are 15 yet.)
I just had my sister check their credit scores via credit sesame, and she's requesting their free credit reports but for some reason couldn't access them online.
Via credit sesame, the older two had scores of 750 or above. They are ages 21, 19, and 16. The youngest one had no score yet, but we just added her a few months ago.
And this was not AMEX, but I added my 14 year old as an AU on two Chase cards when he was 12. According to CreditSesame, he's got an 827. I know credit sesame is an estimate, but even if they're off by 100 points, the boy has a great start!
And AMEX targeted him for a PRG with a 50,000 point bonus this week
As an earlier poster noted, Chase does not take DOB or SSN, so it is being matched up by name and address. Easy to see how errors on your credit report could occur if they're matching up that way.
Anita