I was born with a 9 year amazing gift of the ability to handle toddler tantrums. That last year was hell on earth. Also. Don't make a job out of something you just happen to be good at. Especially if you don't like the main component of it. I made a huge mistake 10 years ago. Anyways. I digress.
4-5 years old? They will be chatty. Very very chatty. They will touch you a lot and want to show you their classroom and play games with you. They will expect you to compliment them and think they are amazeballs. They might surprise you with how smart they can be and then they will throw a block at someone or start crying because their dolls head fell off.
The closer they are to 5, the more they will be into social games (think "You can't come to my birthday party!!") but they might behave better due to the presence of visitors (the social game of pretending to be well behaved in front of strangers to gain trust). The closer they are to 4 years old, the more nice they will be when it comes to social skills. They will be right in the middle of learning about empathy but before they learn to use it against others.
4 year olds are pretty tame and sweet and often enjoy school and showing off what they can do to strangers, 5 year olds have big kid complex but are also very smart and can be challenged in a lot of really neat ways that 4's can't be. There probably won't be too much crying but that also depends on how much of a handle the teachers have on the classroom. If there isn't a strong leader, well, you can't expect 4-5 year olds to react well without one. This age group is also old enough to care for their bodily needs, so wipe their own noses, use the potty and wash their own hands. They are usually pretty good at hygiene at this age too. You can also be firm and direct with this age, but get down on their level when talking to them. Don't want to hold their hand? A little fib goes a long way. "No thank you. My hand hurts, I don't want to hold your hand." Don't want to read them a story? "I don't want to read a story right now. What else would you like to do together?" Kid being obnoxious and all up on your grill? "I need you to walk away and find something else to do please."
They should be on a pretty solid schedule at this time in the school year, so you would probably be doing things like circle time, story time, free play, outside time, snack time, activities time, and then lunch and naptime. My guess is you will get there in the morning either for snack and circle time or right after that. Circle time is when everyone sits together and you do a teacher led activity that is usually theme based. Don't let anyone sit on your lap. I know you wouldn't want that anyway but kids can and will just plop down in it. Just say "I need you to sit on the floor (or wherever they are supposed to be), please." The kids should all be getting their own snack stuff and taking care of it and their own messes. You won't be required to do anything with that. That would be against the rules. Free play is when the kids get to choose where they play. Activities time is when they will do art, sensory, and other small group activities. Try to get on the art activity if they make you do an activity. Kids really like art and they will be the most well behaved here. You can ask them questions about their art and see the creative process and child development through art too.
This got really long. I am so sorry. Let me know if you have any other questions!!