I deal with different personalities every day in my business and I've learned a lot about behaviors over the years. I no longer believe, as I did 10 years ago, that all people are truthful, upstanding, honest, kind, and cordial. This I've learned the hard way.
I have servers who come back into the kitchen in tears because customers have treated them badly. I do not allow them to react harshly to the customers and they know this. I try to ascertain what the problem is by talking to the customer and getting their story. It's easy for me, I just tell them I'm sorry for their inconvenience and give them their dinner for free and apologize profusely.
On the other hand, I've had customers who have put their hands on my servers while berating them in front of a packed house. I've had to remove those customers and will do so any time it ever happens.
Servers are not servants! They are people too. They have families, husbands, babysitters, mortgages, doctor bills, broken pipes, etc. Some people think because they are a paying customer the workers should take whatever crap is dished out to them.
I'm not saying you did that, what I'm saying is the parent in front of you might have without you knowing. The 3 parents in front of you may have. This person knows nothing of you. She doesn't know if you are a parent who is chronically late who doesn't give a hoot about the child care worker.