It’s so hard to know. I’ve met more than my share of parents whose little serial killers in training get greatly offended should anyone dare to comment on their child’s behavior.
If the other passengers weren’t bothered by it and corroborated the mother’s account, the the flight attendant was out of line.
OTOH, chances are SHE wasn’t having the best day either. Unfortunately for her, she’s in an occupation that does not allow the luxury of irritability on the job.
"And she said, no, she was tired, she'd been stranded at the airport all day, and she did not want to hear it."