According to The Sun's Livvi Sefton, Ronaldo was seen on camera in conversation with the two youngsters, one of whom said "For me, you are the best in the world and Messi is..."
"...Bad" came Ronaldo's response, before the other mascot added, "The worst! The worst!"
The forward struck twice in the win, a much-needed boost as he had previously netted just four goals in La Liga all season.
Messi also netted a brace on Sunday as Barcelona beat Real Betis 5-0, taking him to 19 La Liga strikes this season and 25 overall:
The pair have been vying for the position of best in the world for over a decade, and some would argue they're also in contention for consideration as the best of all time.
Ronaldo certainly endorsed the latter after picking up his fifth Ballon d'Or in December to move level with Messi:
Their rivalry has always appeared to be a friendly one, though, spurred on by the remarkable feats they consistently achieve and their passionate fanbases rather than any personal dislike.
That said, it's good for Ronaldo he followed up his joke with a strong performance—had he and Real struggled as they have on numerous occasions this season, it could have backfired in humiliating fashion.