What to Look For/Ask in Preschool Interview.

I'd would ask what their staff to child ratio is and how many children attend total. How long the teachers have been working there? Do you get to see the preschool working? If so, that's a great thing because you can observe interactions and go with your gut.

What is their recommendation in terms of a drop off routine. Do they support you coming into the classroom or do they like a quick drop off. What are their discipline methods? Do they match yours?

What does a daily routine look like? Is there an academic focus or is the program play based? How do they handle children who do not want to participate in structured activities?

Preschool is a really wonderful experience. The first times of drop off will be hard for you, but as soon as you're little one comes home telling you about new friends and brings home art he's made it becomes so much fun. Know that he may be really excited and love it and the drop off will be easy at first and then he might have a hard time with drop off as it loses a little of it's novelty. All of that is perfectly normal at that age and will pass.

You're doing a good thing for him!

OK so this is how it went when my kids went to nursery school back in the
dark ages. They went to a school in town that had been there for 30 years.
Friends all loved, kids did well. We all had complete faith in the teachers
that they knew how to handle all problems that came up. If anything came
up we discussed it at the time. We did not overthink everything and it seems that is the norm today for some reason. My advice to you, is if you
show your son that you are anxious, it will rub off on him. He will then start
to wonder why. So Mom put a smile on your face, be proud of the job you
have done. You will have a tear in your eye that first day, but your heart
will burst with pride. It really is exciting to watch them grow and achieve
so much in their young life.

You want to know how the day is scheduled - it is often easiest to just ask what a typical day will involve (circle time, free play, snacks, structured time etc), the student/teacher ratio (minimum will be set by your state), are the teachers certified? how long have they been there? What is staff turnover like? Can you pack your own lunch/snacks? If they provide snacks, what are they like and do you need to participate (if you are concerned about nutrition)? How much opportunity for free play is there? What philosophy of discipline do they use (time outs, positive discipline, punishment etc)? How often do they have snow days/delays? How sick can he be and still go (runny nose, how long fever free, etc)? Can they give you references (and call those parents)? How do transitions generally go for kids who are new to preschool and will you have input if not going smoothly? Can you drop by to observe at any time (you should be welcome to do this)? What sort of 'academic' program to they do?
Good luck, preschool is a great socialization experience.

I don't know about the certification/liscensing because it varies by state. What you do want to know is what the staff to child ratio is. How do they handle discipline? If food allergies are an issue, are they able to accommodate? How do they handle incidents (like biting, either by your child or another who has bitten your child). Are both sets of parents notified or just the parents of the injured child? What kind of physical activity will they get and is it daily? How do they handle potty times. Do they need to be fully trained, do they take them at a scheduled time or only when they ask to go? Ask any questions that concern you. No question is stupid.
Good luck mom! It's an exciting step!