This is an essential question that you need to find the answer to before the end of the first day. You 100% cannot rely on the certainty of a 5 year old, even if they sound like they know what they are talking about...always double check with the parents!
Before the first day I make little cards with the student's name, teacher's name, and parents phone #. If they are taking the bus then I put their address on there as well. The first day of school is so chaotic for you and for them and you shouldn't just rely on your memory to tell you where they need to be.
You can buy little cut outs like these, found at Teacher Heaven. I laminate them and pin them to their back packs sometime throughout the first day. You can use a variety of other shapes for walkers, parent pickups, after school care, etc. You'll also need to change them out if they'll get home another way the second day.
I have a poster like this found at AZlearningbug that I keep by the door. I usually wait about a week before filling it out, just to give things a chance to settle down. But once it's up, it's a great way to keep other teacher's and staff informed if you have to be away during dismissal...just make sure you keep it updated!