The astrophysicist retained his childlike sense of wonder and never tired of looking at the stars in the night sky

It has a positive connotation, suggesting the astrophysicist’s long-lasting and innocent fascination with the universe.

Explanation:

Connotation refers to the broad display of positive and negative meaning that most words have, whereas denotation refers to the literal definition of a word.

Although the word childlike may seem to have a negative denotation itself, especially when referring to an adult, in the context of this sentence, it has a positive meaning as it's connected to the idea of a sense of wonder with the universe, which seems to be helpful in his line of work.