This article on the experience of sperm donor siblings appeared just recently:
“I have two moms”, my son, O, informed me recently. O is four-and-a-half years old and knows we are different from other families, and he’s okay with that. At this stage, I don’t delve too much into our origin story, but I do occasionally ask him whether he has a Dad. “No, I have a Mommy and a Baba,” he replies, with a shrug and smile.