ITA.... Again I have a similar story from a friend. Luckily CPS didn't come knocking on her door.
My friend was shopping at Michael's (an arts and crafts store) with her 2 kids, about 5 & 7 at the time if I remember correctly how long it has been.
Her oldest, the DD, wanted something and the mom didn't buy it. Her DD started screaming so my friend carried her DD out of the store. She put her DD in her booster, the DS in his and started to leave. Her DD unfastened her seat belt, laid down in the van floor and was kicking and screaming.
This friend does not spank. She decided to ignore the tantrum so she unbuckled her DS, got out of the van with him and stood outside the van while her DD kicked, screamed etc inside the van. someone came up (I don't remember if she said they drove up and parked, or walked up and got into a parked car) and sat in their car a long time just watching her. The person in the car then started dialing their phone. My friend figured the person had called the police, so she put her DS in his booster and forcefully placed her DD in her booster and buckled her in. As she left the parking lot, she saw 2 police cars enter the lot (from another entrance I believe).
She didn't get a mile down the road before her DD unfastened her seatbelt again and threw herself to the floor of the van kicking and screaming. The mother pulled to the side of the road, grabbed her DD and yelled at her to sit down, buckle up and not move until they got home. The mother was so afraid that the police would see the DD jumping around if she kept going, but was afraid they would see them on the side of the road and stop too.
This is the one and only time the mother has ever yelled at one of her kids. She was horrified that she had damaged her DD. She was worried for weeks that the police or CPS would show up at her door, and if the nosy busy body had got their license plate, they probably would have shown up.
I can totally relate this story to myself. There have been many times where I have had to do similiar things with my 4 year old. I have learned that the best way to stop it tantrum is to ignore it. If that means I have to leave him to flip himself around our van for a few minutes before he calms down, then I will. Its happened more times than I'd like to count. I worry that someone may think that I am abusing him, but if you don't have a child like that then you could never understand.
I have spanked my 2 other children when they were younger. I don't do it with my youngest because it would not accomplish anything, and only make it worse.