I don't think I would go from love to hate, as I've never hated anyone. It's just that my love would be lost.

As for a toddler not understanding permanency, that may be. However I don't really subscribe to the idea of claiming something is true (e.g. unconditional love), and then later amending it when permanency is more fully grasped. Similarly, I'm clear from the very beginning that Santa Claus is a fairy tale. I want my children to trust me, and in my eyes trust isn't earned by lying, even when the reason is ageism.