I've been petsitting
for my daughter. Dogs, cats, one indoor, one outdoor, a kitten and a guinea pig. She has chickens, but she had them set up for while they are gone. I checked on them yesterday, to be sure they still had food and water. I don't let them out when I'm there, because I'm scared to death a predator will get them. There are coyotes, bobcats, foxes, and hawks to watch for. I went in the caged coop to check the food. I hadn't thought about it, and was wearing sandals. I painted my toenails before I went to Maine. As I added food to the feeder, several of the hens started slam pecking my feet. They put a lot of effort into each poke. Ow. Luckily, they were more interested in food and after a couple of seconds of toe frenzy, they came to their senses. While I was filling the feeder, I was surprised to see a tiny chick pop out from under the coop structure, and disappear right back under it. I feed the chickens once in awhile, but had to figure out how to get into the coop. After I figured that out, I gave the chicks (at least 2) and the hen that was in with them food and water. I texted my daughter and she had no idea. I knew she thought a hen was hiding a nest somewhere, but she hadn't found it. I think they'll be okay in the coop till tomorrow. I thought about trying to catch them, and putting them in the smaller section of the coop, but it'd probably be hard on them. Always a surprise over there 
= new reply since forum marked as read
I brought a pair of old shoes to slip on and peanuts to bribe them. Put a small waterer in the nursery, and made sure the other chickens have what they need. When I discovered the chicks yesterday, I noticed a pile of eggs in one corner and left them. Today, when I put waterer and food in, the eggs were covered with dirt, still piled. And there is another hen in the far corner hunkered down. Maybe it's a fad! I still heard peeps, so the chicks are still there
I didn't know chickens will cover their eggs. I read either because of inexperience or crowding. The coop is roomy. The coop inside the fence has several nesting boxes about 3' off the ground, with plenty of access and privacy. But they don't use that. I don't usually have to tend to them, and I learn something new almost every time. Especially. I don't want chickens!
They aren't supposed to do it.
Maybe you spooked them since they don't know you.
But I know nothing about chicken psychology.
Was not covered in grad school. 
https://blog.omlet.us/2019/08/20/why-chickens-hide-their-eggs-and-how-to-stop-them-doing-it/