Holy cow. Helecoptor parenting is out of control.
I would let my children go, and I would have taken no for an answer in the first place; my children have special needs, and I would still let them go without me.
This kind of thing just makes me crazy. I would not put up with it if I were the teachers, and would have just said "we will miss little Johnny at the field trip" and let these nutty parents watch thier child at home for the day so that everything was just perfect for them. If everyone cannot cut in line, then nobody can, or we do not have a line any more, we have chaos, and this is the same thing. Kids get bumped, brused, hurt, have bad days, and have times when they have to learn to be alone and independent and it will not always be rainbows and butterflies. Have you seen an 18 year old who just had a bad experience for the first time in thier life? The 5 year old fit happens then, and it is so much more misserable for an 18 year old toddler to learn that they can't have what they want every second of every day.
My husband and I are in our 50's. He is an upper level manager for his firm and a Navy Commander. He has been sharing with me how stupid the parents of his youngest employees and navy officers and enlisteds look when Mom and Dad call to complain about little Johnny's lunch break, or the accomodations in thier war zone rooms in Iraq. Seriously? When does it stop? The answer is...if we let it go on, it does not stop, and Mommy and Daddy get upset when Johnny does not like the food he gets in a war zone. Uhg....