letters from Father Christmas

Surveying a newer entry in the complex publication history of Tolkien's Letters from Father Christmas, I note that this one claims to be the first collection of the complete surviving entries of the letters that F.C. (Santa Claus as he's known stateside) wrote to the Tolkien children in response to their own.

And it also occurred to me, as it also includes reproductions of the postal envelopes (Tolkien conspired with the postman to have them delivered), I can figure out something I've never seen systematically discussed: what ages the children received letters at. How old does a child have to be before they can appreciate the magic of this, and then at what age do these letters cease to be credible?

Tolkien had four children, in order John, Michael, Christopher, and Priscilla. Three of them were born in October or November, but the letters appear to have been sent just before Christmas, so I'll assume after their birthdays in each case.

The first letter, pretty simple, is to John in 1920, aged 3. Michael's first surviving letter is in 1924 when he was 4, but it reads as if it's not his first. Christopher is added to the address of a joint letter in 1926 when he was 2, and Priscilla first appears by name in 1929 when she was but 6 months. But again these are not separate letters to them individually.

The last letter naming John and Michael is in 1932 when they were 15 and 12 respectively, and there's a later letter of that year addressed to Christopher and Priscilla only. Christopher lasts until 1937 when he was 13, and Priscilla to 1943 when she was 14. One suspects this is more because she was still hanging up a stocking for Christmas treats than because she still believed in Father Christmas at that age.