Someone told me calling someone childish is just a nice way of calling them retarded. Is that true?

“Childish” is calling them selfish!
“Child like” is playful and we all need to play!

No, the term childish is more accurately calling the person immature.

never heard that before.

Nope....nothing like...

Not true..

No, it isn’t. It’s more a synonym for “immature”. “Retarded” is the old term for someone who is “slow” or intellectually challenged. That’s nothing to do with simply being a child.

Slightly yes