I said "since their childhood." ^_^ What I meant was that it didn't sit well with Disney or Egmont (who published A Letter From Home) to imply that Hortense and Quackmore would just have cut all connections to their children after they grew up, given that they never show up at family gatherings or at Christmas, are rever referred to and never even call. After all, with all the times Donald have been in trouble (and it's often even been public knowledge that he was, given how he tends to gather a lot of attention), they would have come across as pretty heartless parents to never even bother to contact him and ask if he was all right.
That said, several stories do make references to Donald having largely grown up on Grandma Duck's farm. And Grandma Duck is a definite presence in the comics, probably the only major character from the Barks stories to never have made an appearance in DuckTales, for whatever reason.