Auto and I were just talking about this and she made a good point. In the case of kids who are very clingy, it's even more important to expose them to people coming and going. Sooner or later, they'll have their first relationship and if they're really clingy, they'll fall really hard and fast. This will likely scare the person off, and there's a strong chance the kid will take it as a personal rejection, internalizing it. That's far more detrimental than the pain of exposure early on.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker