Double check the bag and make sure you have PINE shavings and NOT CEDAR.
I have experienced sneezing in my flock from environmental factors (dust etc.) as well as from illness.
Time will tell the difference. Watch them closely (sounds like you already are, so that's good). See if the sneezing increases in frequency. See if the sneezing spreads to other chicks. See if ANY other possible symptoms develop. Look at eyes and nostrils. Even take a pic of your chicks faces up close, then in a few days when you think maybe you might see something unusual, you can compare to the pic of when they seemed healthy and normal to be sure. Eventually chicks with respiratory problems often start breathing with their mouth open (just like when you have a cold and your nose is clogged up). You will be able to hear wheezing. When I had one that was particularly bad, it sounded like the chick was snoring all the time. She ate and drank, but clearly breathing normally was a struggle. I had a chicken once who got squinty eyes, it was from sinus pressure.
If it's environmental, it will just be an occasional sneeze. Nothing more, nothing less. Just like when you get a tickle or a bit of dust or lint or something in your nose. One and done. Chickens kick up dust, live in dust, have dusty bedding, take dust baths, the occasional sneeze happens. I feel like for one reason or another some birds are more sensitive than others. I have one bird I feel like I hear sneeze once a day, and others I swear have never sneezed in their lives.
If it's just an occasional sneeze, don't worry. If it seems to be progressing, or you notice anything else, it's a sign of a bigger problem. Post updates. There are lots of folks on here who can help. I certainly accredit the life of a once sick chick to the members on BYC who helped me treat her.