When my youngest turned 3, we handled it by.....
.......having another.
We now have 4 kids, so I think the freedom from diapers will mean more time to shuttle them off to soccer practice and ballet lessons. I think I will handle the changes by concentrating on what my kids are doing now and what they will be doing in the future. It seems like a good distraction from thinking about how they once were and will never be again.