Yes, I am looking for the word that would mean "great" or "fantastic" that might be used to convey a parent's pride in their adult child (proud of their virtues, accomplishments, character, etc)
That complicates things as Polish parents tend to not do that that much about their adult children.
Do you mean talking to the children themselves or to other people?
But the idea of a Polish person calling their adult child "wspaniały" seems kind of odd to me. Native speakers will have to say what parents say then because I don't have much clue.
In talking to other people, if they're proud of their children they're more likely to list their accomplishments and/or add wspaniały or somesuch to particular accomplishments and not make blanket character statements.