Is there any problem with a Google or Microsoft calendar? Free and app supported on pretty much everything.
I understand your intent, but I reckon kids know really early on. My daughter has been boy crazy since 5, so I never bothered with "or a girlfriend" type comments. But we do instill in her regularly that love is love and partners come in all types.
/r/woodworking is debating going back to normal, or posting pictures of Norm Abrams and Nick Offerman. I'll let you guess which one is winning.