I don't think so happiness is relative so I think no we can't

No they can't

Yes they can... But the value isn't as visible to them compared to a person that has been through all the lows. Imagine a fairytale princess or something and how happy they are. Your question can be switched to: can a person be rich if they have never experienced poverty? You'd find a similar answer.

Beashmur sad agatmogn ayakm eyalk new😝😝😝

Kind of a paradox But No they don't know what sadness means which means they don't appreciate their happiness so they will eventually become sad.

when sadness doesn't exist anymore, there is nothing to consider happy ...this existence becomes just the new "normal way" of living.

Nope we can't appreciate happiness if we aren't sad