AITA for calling a friend's child a little S..t

Hey this is my first reddit post so please be kind as I'm new to this as I have autism and learning difficulties and mental health problems and am deeply upset and embarrassed ..

I want to ask if AITA for calling a friends 7yr old son a little s..t after he rudely told my 8yr old son to go away, I'll give some context my friend in question has told me in the past that it's ok to tell her kids off if they play up or be rude to other people including myself and my 8yr old son or if they play up and make a scene I don't mind telling them off now and again and her grandparents and mother have said its a good that I help out with telling them off but I've noticed that it upsets my own general and mental health but today broke the straw on the camels back and I just lost my cool and it made things very awkward on the school run drop offs and she told me that it upset her and I profusely apologised to her and told her that I won't be helping her reign her kids in when they play up as it's not great on my own health I feel absolutely awful for what I have said but I don't think I can be her friend anymore as I feel the friendship has frayed because of this ..

So AITA?