Remove all the bedding. Put them on a towel or some grippy shelf paper. Give them a day and see if they are still sneezing. This will help you figure out if it’s just dusty bedding or if something else is going on.
x2. Hopefully it's all fine, and no meds needed.
Keep everything related to them separate from your other birds!!! If it is an infection, keep it in that group only!
And if it's an infection, get testing done (swabs for Mycoplasma) at your state vet lab.
unless they are outside it is most likely to dusty for some reason like brooder isn't being cleaned often enough or theirs just a lot of dust in the room, you may need to clean the brooder more often or area the brooder is being kept.
It could be some type of Virus which antibiotics don't really help unless they develop a secondary infection,you just have to keep their nostrils clear, there are a few others like mentioned by others like MG but not sure on how to get that testing done.
if brooder is small or theres lots of chicks they are going to need more cleaning no matter what you use, another suggestion is getting them off the heat lamp, mine at 2-3 days old are usually only wanting it on during the night as their feathers haven't come in yet but as soon as they get some of their feathers they have been fine without it usually by days 5-7 even at night. a broody raised is out exploring and away from heat source at a day old. you just watch, Also I don't use those 250 watt brooder just a normal 60 watt incandescent bulb it really costs less to run while providing sufficient warmth and don't make as much dust in the brooder